diff --git a/C/opening_learner/Makefile b/C/opening_learner/Makefile
new file mode 100644
index 0000000..aa0546e
--- /dev/null
+++ b/C/opening_learner/Makefile
@@ -0,0 +1,30 @@
+CC := gcc
+CFLAGS := -O2 -Wall -Wextra -std=c11
+
+# SDL2 flags: require sdl2-config (no fallback)
+SDL2CONF := $(shell command -v sdl2-config 2>/dev/null)
+ifeq ($(SDL2CONF),)
+$(error sdl2-config not found. Please install SDL2 development package.)
+endif
+SDL_CFLAGS := $(shell sdl2-config --cflags)
+SDL_LDFLAGS := $(shell sdl2-config --libs)
+
+SRC := main.c gui.c engine.c chess.c mistakes.c
+OBJ := $(SRC:.c=.o)
+BIN := opening_learner
+
+.PHONY: all clean run
+
+all: $(BIN)
+
+$(BIN): $(OBJ)
+	$(CC) $(CFLAGS) -o $@ $^ $(SDL_LDFLAGS)
+
+%.o: %.c
+	$(CC) $(CFLAGS) $(SDL_CFLAGS) -c -o $@ $<
+
+run: $(BIN)
+	./$(BIN)
+
+clean:
+	rm -f $(OBJ) $(BIN)
diff --git a/C/opening_learner/README.md b/C/opening_learner/README.md
new file mode 100644
index 0000000..31176c2
--- /dev/null
+++ b/C/opening_learner/README.md
@@ -0,0 +1,26 @@
+# Opening Learner (C + SDL2)
+
+- Click a piece, then click a destination to move.
+- Thick board outline, board uses non-pure colors.
+- Uses local Stockfish or asmfish via UCI.
+- Logs mistakes to `mistakes.txt` and lets you revisit them with the `m` key.
+
+Build and check:
+
+```sh
+./check_build.sh
+```
+
+Run:
+
+```sh
+./opening_learner
+```
+
+Tips:
+- ESC clears selection.
+- Press `m` to cycle to a stored mistake position and practice the best move there.
+- If you play Black, the board flips so Black is at the bottom.
+
+Notes:
+- Rendering avoids TTF dependency; pieces are clear, high-contrast geometric glyphs.
diff --git a/C/opening_learner/check_build.sh b/C/opening_learner/check_build.sh
new file mode 100755
index 0000000..e6ab5b2
--- /dev/null
+++ b/C/opening_learner/check_build.sh
@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+cd "$(dirname "$0")"
+
+echo "Checking for engine (stockfish or asmfish)"
+if command -v stockfish >/dev/null 2>&1; then
+  echo "Found stockfish"
+elif command -v asmfish >/dev/null 2>&1; then
+  echo "Found asmfish"
+else
+  echo "Error: Neither stockfish nor asmfish found in PATH." >&2
+  exit 1
+fi
+
+echo "Checking for SDL2 dev (sdl2-config)"
+if command -v sdl2-config >/dev/null 2>&1; then
+  echo "Found sdl2-config"
+else
+  echo "Error: sdl2-config not found. Install SDL2 dev (e.g., libsdl2-dev)." >&2
+  exit 2
+fi
+
+echo "Building project"
+make clean
+make -j
+
+echo "Build OK"
diff --git a/C/opening_learner/chess.c b/C/opening_learner/chess.c
new file mode 100644
index 0000000..f5e0ed2
--- /dev/null
+++ b/C/opening_learner/chess.c
@@ -0,0 +1,296 @@
+#include "chess.h"
+#include <string.h>
+#include <stdio.h>
+#include <ctype.h>
+#include <stdlib.h>
+
+static const int knight_offsets[8] = {15, 17, -15, -17, 10, -10, 6, -6};
+static const int bishop_dirs[4] = {9, 7, -9, -7};
+static const int rook_dirs[4] = {8, -8, 1, -1};
+static const int king_dirs[8] = {8,-8,1,-1,9,7,-9,-7};
+
+static inline int file_of(int sq){return sq%8;}
+static inline int rank_of(int sq){return sq/8;}
+static inline bool on_board(int sq){return sq>=0 && sq<64;}
+static inline bool same_color(char a, char b){return (isupper(a)&&isupper(b))||(islower(a)&&islower(b));}
+static inline bool is_white(char p){return isupper((unsigned char)p);} 
+
+void chess_init_start(Position *pos){
+    // a1..h1 (0..7) are white back rank; rank 8 at indexes 56..63 are black back rank
+    const char *start = "RNBQKBNRPPPPPPPP................................pppppppprnbqkbnr";
+    for (int i=0;i<64;i++) pos->board[i] = start[i];
+    pos->white_to_move = true;
+    pos->castle_wk = pos->castle_wq = pos->castle_bk = pos->castle_bq = true;
+    pos->ep_square = -1; pos->halfmove_clock = 0; pos->fullmove_number = 1;
+}
+
+void chess_copy(Position *dst, const Position *src){ *dst = *src; }
+
+static bool is_empty(const Position *p, int sq){ return p->board[sq]=='.'; }
+
+bool chess_square_attacked(const Position *pos, int sq, bool by_white){
+    // pawns
+    int r = rank_of(sq), f = file_of(sq);
+    if (by_white){
+        int s1 = (r-1)*8 + (f-1); if (f>0 && r>0 && on_board(s1) && pos->board[s1]=='P') return true;
+        int s2 = (r-1)*8 + (f+1); if (f<7 && r>0 && on_board(s2) && pos->board[s2]=='P') return true;
+    } else {
+        int s1 = (r+1)*8 + (f-1); if (f>0 && r<7 && on_board(s1) && pos->board[s1]=='p') return true;
+        int s2 = (r+1)*8 + (f+1); if (f<7 && r<7 && on_board(s2) && pos->board[s2]=='p') return true;
+    }
+    // knights
+    for (int i=0;i<8;i++){
+        int t = sq + knight_offsets[i];
+        if (!on_board(t)) continue;
+        int df = file_of(t)-f; int dr = rank_of(t)-r; if (df< -2||df>2||dr<-2||dr>2) continue; // edge wrap guard
+        char pc = pos->board[t];
+        if (by_white && pc=='N') return true;
+        if (!by_white && pc=='n') return true;
+    }
+    // bishops/queens
+    for (int d=0; d<4; d++){
+        int off = bishop_dirs[d]; int t = sq + off;
+        while (on_board(t) && abs(file_of(t)-f)==abs(rank_of(t)-r)){
+            char pc = pos->board[t];
+            if (pc!='.') { if (by_white && (pc=='B'||pc=='Q')) return true; if (!by_white && (pc=='b'||pc=='q')) return true; break; }
+            t += off;
+        }
+    }
+    // rooks/queens
+    for (int d=0; d<4; d++){
+        int off = rook_dirs[d]; int t = sq + off;
+        while (on_board(t) && (file_of(t)==f || rank_of(t)==r)){
+            char pc = pos->board[t];
+            if (pc!='.') { if (by_white && (pc=='R'||pc=='Q')) return true; if (!by_white && (pc=='r'||pc=='q')) return true; break; }
+            t += off;
+        }
+    }
+    // king
+    for (int i=0;i<8;i++){
+        int t=sq+king_dirs[i]; if (!on_board(t)) continue; if (abs(file_of(t)-f)>1||abs(rank_of(t)-r)>1) continue;
+        char pc = pos->board[t]; if (by_white && pc=='K') return true; if (!by_white && pc=='k') return true;
+    }
+    return false;
+}
+
+bool chess_is_in_check(const Position *pos, bool white){
+    int ks = -1; char k = white? 'K' : 'k';
+    for (int i=0;i<64;i++) if (pos->board[i]==k) { ks = i; break; }
+    if (ks==-1) return false; // malformed
+    return chess_square_attacked(pos, ks, !white);
+}
+
+static void add_move_if_legal(const Position *pos, int from, int to, char promo, Move *out, size_t *n, size_t max){
+    if (*n >= max) return;
+    Position tmp; chess_copy(&tmp, pos);
+    Move m = {0}; m.from=from; m.to=to; m.promo=promo; m.moved=pos->board[from]; m.captured=pos->board[to];
+    int prev_ep = tmp.ep_square; m.prev_ep = prev_ep; m.prev_wk=tmp.castle_wk; m.prev_wq=tmp.castle_wq; m.prev_bk=tmp.castle_bk; m.prev_bq=tmp.castle_bq; m.prev_halfmove=tmp.halfmove_clock;
+    if (!chess_make_move(&tmp, &m)) return;
+    if (chess_is_in_check(&tmp, !tmp.white_to_move)) return; // after make, side switched
+    out[(*n)++] = m; // store pseudo move with added flags from make_move
+}
+
+size_t chess_generate_legal_moves(const Position *pos, Move *out, size_t max){
+    size_t n=0;
+    bool white = pos->white_to_move;
+    for (int sq=0; sq<64; sq++){
+        char p = pos->board[sq]; if (p=='.') continue; if (white != is_white(p)) continue;
+        int f=file_of(sq), r=rank_of(sq);
+        switch (tolower(p)){
+            case 'p': {
+                int dir = white? 8 : -8; int start_rank = white? 1 : 6; int prom_rank = white? 6 : 1;
+                int one = sq + dir;
+                if (on_board(one) && is_empty(pos, one)){
+                    if (r==prom_rank){
+                        const char *pr = white? "QRBN" : "qrbn";
+                        for (int i=0;i<4;i++) add_move_if_legal(pos, sq, one, pr[i], out, &n, max);
+                    } else add_move_if_legal(pos, sq, one, 0, out, &n, max);
+                    // two
+                    int two = sq + 2*dir; if (r==start_rank && is_empty(pos, two)) add_move_if_legal(pos, sq, two, 0, out, &n, max);
+                }
+                // captures
+                int caps[2] = { dir+1, dir-1 };
+                for (int i=0;i<2;i++){
+                    int t = sq + caps[i]; if (!on_board(t)) continue; if (abs(file_of(t)-f)!=1) continue;
+                    if (!is_empty(pos, t) && !same_color(pos->board[sq], pos->board[t])){
+                        if (r==prom_rank){ const char *pr = white? "QRBN" : "qrbn"; for (int j=0;j<4;j++) add_move_if_legal(pos, sq, t, pr[j], out, &n, max); }
+                        else add_move_if_legal(pos, sq, t, 0, out, &n, max);
+                    }
+                }
+                // en passant
+                if (pos->ep_square!=-1){
+                    int ep = pos->ep_square; if (abs(file_of(ep)-f)==1 && (ep == sq+dir+1 || ep==sq+dir-1)) add_move_if_legal(pos, sq, ep, 0, out, &n, max);
+                }
+            } break;
+            case 'n': {
+                for (int i=0;i<8;i++){
+                    int t = sq + knight_offsets[i]; if (!on_board(t)) continue; if (abs(file_of(t)-f)>2 || abs(rank_of(t)-r)>2) continue; if (!is_empty(pos, t) && same_color(p, pos->board[t])) continue; add_move_if_legal(pos, sq, t, 0, out, &n, max);
+                }
+            } break;
+            case 'b': {
+                for (int d=0; d<4; d++){
+                    int off = bishop_dirs[d]; int t = sq + off; while (on_board(t) && abs(file_of(t)-f)==abs(rank_of(t)-r)){
+                        if (!is_empty(pos, t)){ if (!same_color(p, pos->board[t])) add_move_if_legal(pos, sq, t, 0, out, &n, max); break; }
+                        add_move_if_legal(pos, sq, t, 0, out, &n, max); t += off;
+                    }
+                }
+            } break;
+            case 'r': {
+                for (int d=0; d<4; d++){
+                    int off = rook_dirs[d]; int t = sq + off; while (on_board(t) && (file_of(t)==f || rank_of(t)==r)){
+                        if (!is_empty(pos, t)){ if (!same_color(p, pos->board[t])) add_move_if_legal(pos, sq, t, 0, out, &n, max); break; }
+                        add_move_if_legal(pos, sq, t, 0, out, &n, max); t += off;
+                    }
+                }
+            } break;
+            case 'q': {
+                for (int d=0; d<4; d++){
+                    int off = bishop_dirs[d]; int t = sq + off; while (on_board(t) && abs(file_of(t)-f)==abs(rank_of(t)-r)){
+                        if (!is_empty(pos, t)){ if (!same_color(p, pos->board[t])) add_move_if_legal(pos, sq, t, 0, out, &n, max); break; }
+                        add_move_if_legal(pos, sq, t, 0, out, &n, max); t += off;
+                    }
+                }
+                for (int d=0; d<4; d++){
+                    int off = rook_dirs[d]; int t = sq + off; while (on_board(t) && (file_of(t)==f || rank_of(t)==r)){
+                        if (!is_empty(pos, t)){ if (!same_color(p, pos->board[t])) add_move_if_legal(pos, sq, t, 0, out, &n, max); break; }
+                        add_move_if_legal(pos, sq, t, 0, out, &n, max); t += off;
+                    }
+                }
+            } break;
+            case 'k': {
+                for (int i=0;i<8;i++){
+                    int t = sq + king_dirs[i]; if (!on_board(t)) continue; if (abs(file_of(t)-f)>1||abs(rank_of(t)-r)>1) continue; if (!is_empty(pos, t) && same_color(p, pos->board[t])) continue; add_move_if_legal(pos, sq, t, 0, out, &n, max);
+                }
+                // castling
+                if (white){
+                    if (pos->castle_wk && pos->board[5]=='.' && pos->board[6]=='.' && !chess_square_attacked(pos,4,false) && !chess_square_attacked(pos,5,false) && !chess_square_attacked(pos,6,false)) add_move_if_legal(pos, 4, 6, 0, out, &n, max);
+                    if (pos->castle_wq && pos->board[3]=='.' && pos->board[2]=='.' && pos->board[1]=='.' && !chess_square_attacked(pos,4,false) && !chess_square_attacked(pos,3,false) && !chess_square_attacked(pos,2,false)) add_move_if_legal(pos, 4, 2, 0, out, &n, max);
+                } else {
+                    if (pos->castle_bk && pos->board[61]=='.' && pos->board[62]=='.' && !chess_square_attacked(pos,60,true) && !chess_square_attacked(pos,61,true) && !chess_square_attacked(pos,62,true)) add_move_if_legal(pos, 60, 62, 0, out, &n, max);
+                    if (pos->castle_bq && pos->board[59]=='.' && pos->board[58]=='.' && pos->board[57]=='.' && !chess_square_attacked(pos,60,true) && !chess_square_attacked(pos,59,true) && !chess_square_attacked(pos,58,true)) add_move_if_legal(pos, 60, 58, 0, out, &n, max);
+                }
+            } break;
+        }
+    }
+    return n;
+}
+
+bool chess_make_move(Position *pos, Move *m){
+    m->is_castle=false; m->is_enpassant=false;
+    char p = pos->board[m->from]; char tgt = pos->board[m->to];
+    if (p=='.') return false;
+    // handle special: en passant capture
+    if (tolower(p)=='p' && m->to == pos->ep_square && file_of(m->to)!=file_of(m->from) && tgt=='.'){
+        m->is_enpassant = true;
+        int cap_sq = pos->white_to_move ? (m->to - 8) : (m->to + 8);
+        m->captured = pos->board[cap_sq]; pos->board[cap_sq]='.';
+    }
+
+    // move piece
+    pos->board[m->to] = p;
+    pos->board[m->from] = '.';
+
+    // promotion
+    if (tolower(p)=='p' && m->promo){ pos->board[m->to] = m->promo; }
+
+    // castling rook move
+    if (tolower(p)=='k'){
+        int from = m->from, to = m->to;
+        if (from==4 && to==6){ pos->board[5]='R'; pos->board[7]='.'; m->is_castle=true; }
+        else if (from==4 && to==2){ pos->board[3]='R'; pos->board[0]='.'; m->is_castle=true; }
+        else if (from==60 && to==62){ pos->board[61]='r'; pos->board[63]='.'; m->is_castle=true; }
+        else if (from==60 && to==58){ pos->board[59]='r'; pos->board[56]='.'; m->is_castle=true; }
+    }
+
+    // update castling rights
+    if (m->from==0||m->to==0) pos->castle_wq=false;
+    if (m->from==7||m->to==7) pos->castle_wk=false;
+    if (m->from==56||m->to==56) pos->castle_bq=false;
+    if (m->from==63||m->to==63) pos->castle_bk=false;
+    if (tolower(p)=='k'){ if (is_white(p)) { pos->castle_wk=pos->castle_wq=false;} else {pos->castle_bk=pos->castle_bq=false;} }
+
+    // update ep square
+    pos->ep_square = -1;
+    if (tolower(p)=='p'){
+        int df = rank_of(m->to) - rank_of(m->from);
+        if (df==2 || df==-2){ pos->ep_square = (m->from + m->to)/2; }
+    }
+
+    // halfmove clock
+    if (tolower(p)=='p' || tgt!='.') pos->halfmove_clock = 0; else pos->halfmove_clock++;
+
+    // side to move
+    pos->white_to_move = !pos->white_to_move; if (pos->white_to_move) pos->fullmove_number++;
+
+    return true;
+}
+
+void chess_unmake_move(Position *pos, const Move *m){
+    pos->white_to_move = !pos->white_to_move; if (!pos->white_to_move) pos->fullmove_number--;
+    // restore halfmove/flags
+    pos->ep_square = m->prev_ep;
+    pos->castle_wk = m->prev_wk; pos->castle_wq = m->prev_wq; pos->castle_bk = m->prev_bk; pos->castle_bq = m->prev_bq;
+    pos->halfmove_clock = m->prev_halfmove;
+
+    char p = m->moved;
+    // undo promotions
+    if (tolower(p)=='p' && m->promo){ p = is_white(p)? 'P':'p'; }
+
+    pos->board[m->from] = p;
+    pos->board[m->to] = m->captured? m->captured : '.';
+    if (m->is_enpassant){ int cap_sq = pos->white_to_move ? (m->to - 8) : (m->to + 8); pos->board[m->to]='.'; pos->board[cap_sq]= m->captured; }
+    if (m->is_castle){
+        if (m->from==4 && m->to==6){ pos->board[7]='R'; pos->board[5]='.'; }
+        else if (m->from==4 && m->to==2){ pos->board[0]='R'; pos->board[3]='.'; }
+        else if (m->from==60 && m->to==62){ pos->board[63]='r'; pos->board[61]='.'; }
+        else if (m->from==60 && m->to==58){ pos->board[56]='r'; pos->board[59]='.'; }
+    }
+}
+
+void sq_to_coord(int sq, int *file, int *rank){ if (file) *file=file_of(sq); if (rank) *rank=rank_of(sq); }
+int coord_to_sq(int file, int rank){ return rank*8 + file; }
+
+void move_to_uci(const Move *m, char buf[8]){
+    int f1=file_of(m->from), r1=rank_of(m->from), f2=file_of(m->to), r2=rank_of(m->to);
+    buf[0]='a'+f1; buf[1]='1'+r1; buf[2]='a'+f2; buf[3]='1'+r2; int i=4;
+    if (m->promo){ buf[i++]=tolower(m->promo); }
+    buf[i]='\0';
+}
+
+bool parse_uci_move(const char *s, const Position *pos, Move *out){
+    if (!s || strlen(s)<4) return false;
+    int f1=s[0]-'a', r1=s[1]-'1', f2=s[2]-'a', r2=s[3]-'1'; if (f1<0||f1>7||f2<0||f2>7||r1<0||r1>7||r2<0||r2>7) return false;
+    int from = r1*8+f1, to=r2*8+f2; char promo = s[4]? s[4]:0; if (promo) promo = pos->white_to_move? toupper((unsigned char)promo):tolower((unsigned char)promo);
+    Move list[MAX_MOVES]; size_t n = chess_generate_legal_moves(pos, list, MAX_MOVES);
+    for (size_t i=0;i<n;i++){ if (list[i].from==from && list[i].to==to){ *out = list[i]; out->promo = promo? promo : list[i].promo; return true; } }
+    return false;
+}
+
+bool chess_to_fen(const Position *pos, char *out, size_t outsz){
+    char buf[256]; int idx=0;
+    for (int r=7;r>=0;r--){
+        int empty=0;
+        for (int f=0;f<8;f++){
+            char p = pos->board[r*8+f];
+            if (p=='.') empty++; else { if (empty){ buf[idx++]= '0'+empty; empty=0; } buf[idx++]=p; }
+        }
+        if (empty) buf[idx++]= '0'+empty;
+        if (r) buf[idx++]='/';
+    }
+    buf[idx++]=' ';
+    buf[idx++]= pos->white_to_move ? 'w':'b';
+    buf[idx++]=' ';
+    int start=idx;
+    if (pos->castle_wk) buf[idx++]='K';
+    if (pos->castle_wq) buf[idx++]='Q';
+    if (pos->castle_bk) buf[idx++]='k';
+    if (pos->castle_bq) buf[idx++]='q';
+    if (idx==start) buf[idx++]='-';
+    buf[idx++]=' ';
+    if (pos->ep_square==-1){ buf[idx++]='-'; }
+    else { int f=file_of(pos->ep_square), r=rank_of(pos->ep_square); buf[idx++]='a'+f; buf[idx++]='1'+r; }
+    idx += snprintf(buf+idx, sizeof(buf)-idx, " %d %d", pos->halfmove_clock, pos->fullmove_number);
+    buf[idx]='\0';
+    snprintf(out, outsz, "%s", buf);
+    return true;
+}
diff --git a/C/opening_learner/chess.h b/C/opening_learner/chess.h
new file mode 100644
index 0000000..9c2c9f6
--- /dev/null
+++ b/C/opening_learner/chess.h
@@ -0,0 +1,56 @@
+#ifndef CHESS_H
+#define CHESS_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+// Board is 64 chars, a1=0, b1=1, ..., h8=63
+// Pieces: 'P','N','B','R','Q','K' for white, lowercase for black, '.' empty
+
+typedef struct {
+    char board[64];
+    bool white_to_move;
+    bool castle_wk, castle_wq, castle_bk, castle_bq;
+    int ep_square; // -1 if none
+    int halfmove_clock;
+    int fullmove_number;
+} Position;
+
+typedef struct {
+    int from, to;
+    char promo; // 0 or 'q','r','b','n' (lowercase for black)
+    char captured; // piece captured or 0
+    char moved;    // piece moved
+    bool is_castle;
+    bool is_enpassant;
+    int prev_ep;
+    bool prev_wk, prev_wq, prev_bk, prev_bq;
+    int prev_halfmove;
+} Move;
+
+void chess_init_start(Position *pos);
+void chess_copy(Position *dst, const Position *src);
+
+// Move gen and make/unmake
+size_t chess_generate_legal_moves(const Position *pos, Move *out, size_t max);
+bool chess_make_move(Position *pos, Move *m);
+void chess_unmake_move(Position *pos, const Move *m);
+
+// Utility
+bool chess_is_in_check(const Position *pos, bool white);
+bool chess_square_attacked(const Position *pos, int sq, bool by_white);
+
+// Conversions
+void sq_to_coord(int sq, int *file, int *rank);
+int coord_to_sq(int file, int rank);
+
+// UCI strings like e2e4, with optional promotion char
+void move_to_uci(const Move *m, char buf[8]);
+bool parse_uci_move(const char *s, const Position *pos, Move *out);
+
+// FEN
+bool chess_to_fen(const Position *pos, char *out, size_t outsz);
+
+#define MAX_MOVES 256
+
+#endif
diff --git a/C/opening_learner/chess.o b/C/opening_learner/chess.o
new file mode 100644
index 0000000..ee51fb8
Binary files /dev/null and b/C/opening_learner/chess.o differ
diff --git a/C/opening_learner/engine.c b/C/opening_learner/engine.c
new file mode 100644
index 0000000..c4ce1b0
--- /dev/null
+++ b/C/opening_learner/engine.c
@@ -0,0 +1,141 @@
+#include "engine.h"
+#include <unistd.h>
+#include <fcntl.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <errno.h>
+
+static bool spawn_process(const char *path, Engine *e){
+    int inpipe[2], outpipe[2];
+    if (pipe(inpipe)<0 || pipe(outpipe)<0) return false;
+    pid_t pid = fork();
+    if (pid < 0) return false;
+    if (pid == 0){
+        dup2(inpipe[0], STDIN_FILENO); // child stdin from inpipe[0]
+        dup2(outpipe[1], STDOUT_FILENO); // child stdout to outpipe[1]
+        dup2(outpipe[1], STDERR_FILENO);
+        close(inpipe[0]); close(inpipe[1]); close(outpipe[0]); close(outpipe[1]);
+        execlp(path, path, (char*)NULL);
+        _exit(127);
+    }
+    // parent
+    close(inpipe[0]); close(outpipe[1]);
+    e->pid = pid; e->in_fd = inpipe[1]; e->out_fd = outpipe[0]; e->ready=false;
+    // make out_fd non-blocking for reads with polling
+    int flags = fcntl(e->out_fd, F_GETFL, 0); fcntl(e->out_fd, F_SETFL, flags | O_NONBLOCK);
+    return true;
+}
+
+static bool try_start(Engine *e, const char *name){
+    if (!spawn_process(name, e)) return false;
+    // send UCI init
+    engine_cmd(e, "uci\n");
+    char buf[4096]; int attempts=50; // ~5s total
+    while (attempts--){
+        usleep(100000);
+        ssize_t n = read(e->out_fd, buf, sizeof(buf)-1);
+        if (n>0){
+            buf[n]='\0';
+            if (strstr(buf, "uciok")) { e->ready=true; break; }
+        }
+    }
+    if (!e->ready){ engine_stop(e); return false; }
+    engine_cmd(e, "isready\n");
+    attempts=50;
+    while (attempts--){
+        usleep(100000);
+        ssize_t n = read(e->out_fd, buf, sizeof(buf)-1);
+        if (n>0){ buf[n]='\0'; if (strstr(buf, "readyok")) break; }
+    }
+    return e->ready;
+}
+
+bool engine_start(Engine *e){
+    memset(e, 0, sizeof(*e)); e->pid=-1; e->in_fd=-1; e->out_fd=-1; e->ready=false;
+    if (try_start(e, "stockfish")) return true;
+    if (try_start(e, "asmfish")) return true;
+    return false;
+}
+
+void engine_stop(Engine *e){
+    if (e->in_fd!=-1){ write(e->in_fd, "quit\n", 5); close(e->in_fd); }
+    if (e->out_fd!=-1) close(e->out_fd);
+    if (e->pid>0){ int status; waitpid(e->pid, &status, 0); }
+    e->pid=-1; e->in_fd=e->out_fd=-1; e->ready=false;
+}
+
+bool engine_cmd(Engine *e, const char *cmd){
+    if (e->in_fd==-1) return false;
+    size_t len = strlen(cmd);
+    ssize_t n = write(e->in_fd, cmd, len);
+    if (n < 0) {
+        return false;
+    }
+    return n == (ssize_t)len;
+}
+
+static void position_to_uci(const Position *pos, char *out, size_t outsz){
+    // Send starting position and moves list by comparing with startpos; for simplicity, use FEN always.
+    char fen[256]; chess_to_fen(pos, fen, sizeof(fen));
+    snprintf(out, outsz, "position fen %s\n", fen);
+}
+
+size_t engine_get_top_moves(Engine *e, const Position *pos, EngineMove *out, size_t max){
+    if (!e->ready) return 0;
+    char cmd[512]; position_to_uci(pos, cmd, sizeof(cmd)); engine_cmd(e, cmd);
+    // ask multiPV up to max (cap at 5 as requested)
+    size_t req = max; if (req>5) req=5; char go[128]; snprintf(go, sizeof(go), "setoption name MultiPV value %zu\n", req); engine_cmd(e, go);
+    engine_cmd(e, "go movetime 400\n");
+    char buf[8192]; size_t count=0; int attempts=50;
+    while (attempts--){
+        usleep(100000);
+    ssize_t n = read(e->out_fd, buf, sizeof(buf)-1);
+    if (n<=0) continue;
+    buf[n]='\0';
+        char *line = strtok(buf, "\n");
+        while (line){
+            if (strncmp(line, "info ", 5)==0){
+                // parse "info ... multipv X score cp Y ... pv <uci>"
+                char *mpv = strstr(line, " multipv "); char *score = strstr(line, " score "); char *pv = strstr(line, " pv ");
+                if (mpv && score && pv){
+                    int idx = atoi(mpv+9); if (idx>=1 && (size_t)idx<=req){
+                        int cp=0; if (strstr(score, "cp ")) cp = atoi(strstr(score, "cp ")+3);
+                        char mv[8]={0};
+                        sscanf(pv+4, "%7s", mv);
+                        size_t i = (size_t)idx-1; if (i<req){ out[i].score_cp = cp; snprintf(out[i].uci, sizeof(out[i].uci), "%s", mv); if (i+1>count) count=i+1; }
+                    }
+                }
+            } else if (strncmp(line, "bestmove ", 9)==0){ attempts=0; break; }
+            line = strtok(NULL, "\n");
+        }
+    }
+    // simple sort by score descending (best to worst), keeping empties at end
+    for (size_t i=0;i<count;i++){
+        for (size_t j=i+1;j<count;j++){
+            if (out[j].score_cp > out[i].score_cp){ EngineMove tmp=out[i]; out[i]=out[j]; out[j]=tmp; }
+        }
+    }
+    return count;
+}
+
+bool engine_get_best_move(Engine *e, const Position *pos, char out_uci[8]){
+    if (!e->ready) return false;
+    char cmd[512]; position_to_uci(pos, cmd, sizeof(cmd)); engine_cmd(e, cmd);
+    engine_cmd(e, "go movetime 300\n");
+    char buf[4096]; int attempts=50;
+    while (attempts--){
+        usleep(100000);
+    ssize_t n = read(e->out_fd, buf, sizeof(buf)-1);
+    if (n<=0) continue;
+    buf[n]='\0';
+        char *line = strtok(buf, "\n");
+        while (line){
+            if (strncmp(line, "bestmove ", 9)==0){ sscanf(line+9, "%7s", out_uci); return true; }
+            line = strtok(NULL, "\n");
+        }
+    }
+    return false;
+}
diff --git a/C/opening_learner/engine.h b/C/opening_learner/engine.h
new file mode 100644
index 0000000..092918f
--- /dev/null
+++ b/C/opening_learner/engine.h
@@ -0,0 +1,34 @@
+#ifndef ENGINE_H
+#define ENGINE_H
+
+#include <stddef.h>
+#include <stdbool.h>
+
+#include "chess.h"
+
+typedef struct {
+    int score_cp; // centipawns relative to side to move
+    char uci[8];
+} EngineMove;
+
+typedef struct {
+    int pid;
+    int in_fd;  // write to engine stdin
+    int out_fd; // read from engine stdout
+    bool ready;
+} Engine;
+
+// Start engine: tries stockfish, then asmfish. Returns false if none.
+bool engine_start(Engine *e);
+void engine_stop(Engine *e);
+
+// Synchronous send command
+bool engine_cmd(Engine *e, const char *cmd);
+
+// Ask for top N moves from a position (short fixed time). Returns count.
+size_t engine_get_top_moves(Engine *e, const Position *pos, EngineMove *out, size_t max);
+
+// Ask for best move only.
+bool engine_get_best_move(Engine *e, const Position *pos, char out_uci[8]);
+
+#endif
diff --git a/C/opening_learner/engine.o b/C/opening_learner/engine.o
new file mode 100644
index 0000000..e400c89
Binary files /dev/null and b/C/opening_learner/engine.o differ
diff --git a/C/opening_learner/gui.c b/C/opening_learner/gui.c
new file mode 100644
index 0000000..428315d
--- /dev/null
+++ b/C/opening_learner/gui.c
@@ -0,0 +1,158 @@
+#include "gui.h"
+#include <SDL2/SDL.h>
+#include <stdio.h>
+
+const SDL_Color COLOR_LIGHT = { 238, 238, 210, 255 }; // light square (not pure white)
+const SDL_Color COLOR_DARK  = { 118, 150, 86, 255 };  // dark square (not pure black)
+const SDL_Color COLOR_GRID  = { 20, 20, 20, 255 };    // thick outline
+const SDL_Color COLOR_SEL   = { 200, 50, 50, 200 };   // selection highlight
+const SDL_Color COLOR_TEXT  = { 10, 10, 10, 255 };
+
+static void set_color(SDL_Renderer *r, SDL_Color c) {
+    SDL_SetRenderDrawColor(r, c.r, c.g, c.b, c.a);
+}
+
+bool gui_init(Gui *g, int w, int h, const char *title) {
+    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
+        fprintf(stderr, "SDL_Init error: %s\n", SDL_GetError());
+        return false;
+    }
+    g->window = SDL_CreateWindow(title, SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, w, h, SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE);
+    if (!g->window) {
+        fprintf(stderr, "SDL_CreateWindow error: %s\n", SDL_GetError());
+        return false;
+    }
+    g->renderer = SDL_CreateRenderer(g->window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
+    if (!g->renderer) {
+        fprintf(stderr, "SDL_CreateRenderer error: %s\n", SDL_GetError());
+        return false;
+    }
+    g->win_w = w; g->win_h = h; g->flipped = false;
+    return true;
+}
+
+void gui_destroy(Gui *g) {
+    if (g->renderer) SDL_DestroyRenderer(g->renderer);
+    if (g->window) SDL_DestroyWindow(g->window);
+    SDL_Quit();
+}
+
+void gui_set_flipped(Gui *g, bool flipped) { g->flipped = flipped; }
+
+static void draw_rect(SDL_Renderer *r, int x, int y, int w, int h, SDL_Color c) {
+    set_color(r, c);
+    SDL_Rect rc = { x, y, w, h };
+    SDL_RenderFillRect(r, &rc);
+}
+
+static void draw_outline(SDL_Renderer *r, int x, int y, int w, int h, int thickness, SDL_Color c) {
+    set_color(r, c);
+    for (int i=0;i<thickness;i++) {
+        SDL_Rect rc = { x+i, y+i, w-2*i, h-2*i };
+        SDL_RenderDrawRect(r, &rc);
+    }
+}
+
+static void draw_piece_letter(SDL_Renderer *r, int x, int y, int size, char p) {
+    // Minimal: draw a filled circle/square plus an initial letter approximated with rectangles.
+    // To keep dependencies minimal, no TTF. Ensure contrast: white pieces light, black pieces dark.
+    SDL_Color fill = (p >= 'A' && p <= 'Z') ? (SDL_Color){250, 250, 250, 255} : (SDL_Color){30, 30, 30, 255};
+    SDL_Color glyph = (p >= 'A' && p <= 'Z') ? (SDL_Color){30, 30, 30, 255} : (SDL_Color){240, 240, 240, 255};
+    // Base disk
+    draw_rect(r, x+size*0.15, y+size*0.15, (int)(size*0.7), (int)(size*0.7), fill);
+    // Glyph: draw a simple letter-like mark
+    set_color(r, glyph);
+    // vertical bar
+    SDL_Rect bar1 = { x + size/2 - size/16, y + size/3, size/8, size/3 };
+    SDL_RenderFillRect(r, &bar1);
+    // top bar
+    SDL_Rect bar2 = { x + size/3, y + size/3 - size/10, size/3, size/10 };
+    SDL_RenderFillRect(r, &bar2);
+}
+
+void gui_draw(Gui *g, const char board[64], const GuiSelection *sel, const char *status_line) {
+    SDL_GetWindowSize(g->window, &g->win_w, &g->win_h);
+
+    set_color(g->renderer, (SDL_Color){ 35, 35, 35, 255 });
+    SDL_RenderClear(g->renderer);
+
+    int size = (g->win_w < g->win_h ? g->win_w : g->win_h) - 40; // margins
+    if (size < 200) size = 200;
+    int cell = size / 8;
+    size = cell * 8;
+    int ox = (g->win_w - size)/2;
+    int oy = (g->win_h - size)/2;
+
+    // Board outline (thick)
+    draw_outline(g->renderer, ox-6, oy-6, size+12, size+12, 6, COLOR_GRID);
+
+    // Squares
+    for (int r=0;r<8;r++) {
+        for (int f=0;f<8;f++) {
+            int idx = g->flipped ? (63 - (r*8+f)) : (r*8+f);
+            SDL_Color c = ((r+f)&1) ? COLOR_DARK : COLOR_LIGHT;
+            draw_rect(g->renderer, ox + f*cell, oy + r*cell, cell, cell, c);
+
+            char p = board[idx];
+            if (p != '.' && p != '\0') {
+                draw_piece_letter(g->renderer, ox + f*cell, oy + r*cell, cell, p);
+            }
+        }
+    }
+
+    // Selection overlay
+    if (sel && sel->clicked && sel->from_sq >= 0) {
+        int s = sel->from_sq;
+        int rr = g->flipped ? 7 - (s/8) : (s/8);
+        int ff = g->flipped ? 7 - (s%8) : (s%8);
+        draw_outline(g->renderer, ox + ff*cell+2, oy + rr*cell+2, cell-4, cell-4, 3, COLOR_SEL);
+    }
+
+    // Status strip
+    draw_outline(g->renderer, 10, g->win_h - 40, g->win_w - 20, 30, 2, COLOR_GRID);
+    // Without TTF, we can't render text; draw a minimal indicator bar to signal state.
+    // If status_line indicates success/failure, alter color.
+    SDL_Color bar = { 80, 120, 200, 255 };
+    if (status_line && status_line[0]) {
+        if (SDL_strstr(status_line, "Correct")) bar = (SDL_Color){80, 200, 120, 255};
+        else if (SDL_strstr(status_line, "Wrong")) bar = (SDL_Color){200, 80, 80, 255};
+    }
+    draw_rect(g->renderer, 12, g->win_h - 38, g->win_w - 24, 26, bar);
+
+    SDL_RenderPresent(g->renderer);
+}
+
+int gui_coord_to_sq(Gui *g, int x, int y) {
+    int w, h; SDL_GetWindowSize(g->window, &w, &h);
+    int size = (w < h ? w : h) - 40; if (size < 200) size = 200;
+    int cell = size / 8; size = cell * 8;
+    int ox = (w - size)/2; int oy = (h - size)/2;
+    if (x < ox || y < oy || x >= ox+size || y >= oy+size) return -1;
+    int f = (x - ox) / cell;
+    int r = (y - oy) / cell;
+    int sq = r*8 + f;
+    if (g->flipped) sq = 63 - sq;
+    return sq;
+}
+
+bool gui_poll_move(Gui *g, GuiSelection *sel, bool *quit_requested, int *key_out) {
+    SDL_Event e;
+    bool updated = false;
+    if (key_out) *key_out = 0;
+    while (SDL_PollEvent(&e)) {
+        if (e.type == SDL_QUIT) { if (quit_requested) *quit_requested = true; }
+        else if (e.type == SDL_WINDOWEVENT && e.window.event == SDL_WINDOWEVENT_SIZE_CHANGED) {
+            updated = true;
+        } else if (e.type == SDL_MOUSEBUTTONDOWN && e.button.button == SDL_BUTTON_LEFT) {
+            int sq = gui_coord_to_sq(g, e.button.x, e.button.y);
+            if (sq >= 0) {
+                if (!sel->clicked) { sel->from_sq = sq; sel->to_sq = -1; sel->clicked = true; }
+                else { sel->to_sq = sq; updated = true; }
+            }
+        } else if (e.type == SDL_KEYDOWN) {
+            if (e.key.keysym.sym == SDLK_ESCAPE) { sel->clicked = false; sel->from_sq = sel->to_sq = -1; updated = true; }
+            if (key_out) *key_out = e.key.keysym.sym;
+        }
+    }
+    return updated;
+}
diff --git a/C/opening_learner/gui.h b/C/opening_learner/gui.h
new file mode 100644
index 0000000..c409657
--- /dev/null
+++ b/C/opening_learner/gui.h
@@ -0,0 +1,36 @@
+#ifndef GUI_H
+#define GUI_H
+
+#include <stdbool.h>
+#include <SDL2/SDL.h>
+
+typedef struct {
+    SDL_Window *window;
+    SDL_Renderer *renderer;
+    int win_w, win_h;
+    bool flipped; // true if black at bottom
+} Gui;
+
+typedef struct {
+    int from_sq; // 0..63 or -1
+    int to_sq;   // 0..63 or -1
+    char promo;  // 'q','r','b','n' or 0
+    bool clicked;
+} GuiSelection;
+
+bool gui_init(Gui *g, int w, int h, const char *title);
+void gui_destroy(Gui *g);
+void gui_set_flipped(Gui *g, bool flipped);
+void gui_draw(Gui *g, const char board[64], const GuiSelection *sel, const char *status_line);
+// Returns true if something changed. If a key was pressed, key_out receives SDL_Keycode else 0.
+bool gui_poll_move(Gui *g, GuiSelection *sel, bool *quit_requested, int *key_out);
+int gui_coord_to_sq(Gui *g, int x, int y);
+
+// colors
+extern const SDL_Color COLOR_LIGHT;
+extern const SDL_Color COLOR_DARK;
+extern const SDL_Color COLOR_GRID;
+extern const SDL_Color COLOR_SEL;
+extern const SDL_Color COLOR_TEXT;
+
+#endif
diff --git a/C/opening_learner/gui.o b/C/opening_learner/gui.o
new file mode 100644
index 0000000..46d7ba4
Binary files /dev/null and b/C/opening_learner/gui.o differ
diff --git a/C/opening_learner/main.c b/C/opening_learner/main.c
new file mode 100644
index 0000000..993f89e
--- /dev/null
+++ b/C/opening_learner/main.c
@@ -0,0 +1,193 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+#include <string.h>
+#include <stdbool.h>
+#include <signal.h>
+
+#include "gui.h"
+#include "chess.h"
+#include "engine.h"
+#include "mistakes.h"
+
+typedef struct {
+	Position pos;
+	Engine engine;
+	Gui gui;
+	MistakeList mistakes;
+	bool replay_mode; // allow revisiting mistakes
+	size_t replay_index;
+} App;
+
+static void append_uci(char *line, size_t sz, const char *mv){
+	if (line[0]) strncat(line, " ", sz-1);
+	strncat(line, mv, sz-1);
+}
+
+static void position_push_move_text(Position *pos, const Move *m, char *line, size_t lsz){
+	(void)pos;
+	char u[8]; move_to_uci(m, u);
+	append_uci(line, lsz, u);
+}
+
+static void collect_all_legal_uci(const Position *pos, char list[][8], size_t *n, size_t max){
+	Move mv[MAX_MOVES]; size_t k = chess_generate_legal_moves(pos, mv, MAX_MOVES);
+	*n = 0;
+	for (size_t i=0;i<k && *n<max;i++){ char u[8]; move_to_uci(&mv[i], u); strncpy(list[(*n)++], u, 8); }
+}
+
+static bool uci_in_list(const char *u, char list[][8], size_t n){
+	for (size_t i=0;i<n;i++){
+		if (strncmp(u, list[i], 8)==0) return true;
+	}
+	return false;
+}
+
+static const char *mistake_file_path(){ return "mistakes.txt"; }
+
+int main(){
+	srand((unsigned)time(NULL));
+
+	App app; memset(&app, 0, sizeof(app));
+	mistakes_init(&app.mistakes);
+	mistakes_load(&app.mistakes, mistake_file_path());
+
+	// Avoid SIGPIPE crashes when engine pipe closes
+	signal(SIGPIPE, SIG_IGN);
+
+	if (!gui_init(&app.gui, 720, 760, "Opening Learner")){
+		fprintf(stderr, "GUI init failed.\n");
+		return 1;
+	}
+
+	if (!engine_start(&app.engine)){
+		fprintf(stderr, "Error: Neither stockfish nor asmfish found locally. Please install one.\n");
+		gui_destroy(&app.gui);
+		return 1;
+	}
+
+	// Initialize position
+	chess_init_start(&app.pos);
+
+	// Randomly pick side
+	bool player_is_white = rand()%2==0;
+	gui_set_flipped(&app.gui, !player_is_white);
+
+	// gameplay state
+	char status[128] = "";
+	GuiSelection sel = { .from_sq=-1,.to_sq=-1,.promo=0,.clicked=false };
+	char line_uci[512] = ""; // history of moves uci
+
+	// If white, player moves first
+	bool awaiting_player = player_is_white;
+	char expected_player_move[8] = ""; // best move suggested by engine for player
+	bool quit=false;
+
+	while (!quit){
+		// Show board
+		gui_draw(&app.gui, app.pos.board, &sel, status);
+
+		// Engine to act when it's engine turn
+		if (!awaiting_player){
+			// 2. Ask engine for proposed responses (5)
+			EngineMove props[5]; size_t n = engine_get_top_moves(&app.engine, &app.pos, props, 5);
+			// 3. Sort is done in engine; also collect legal ones not proposed
+			char legal[256][8]; size_t lcnt=0; collect_all_legal_uci(&app.pos, legal, &lcnt, 256);
+			// 4. pick response with decreasing probability
+			size_t total = n;
+			// add non-proposed at the end with minimal priority
+			char pool[300][8]; int weights[300]; size_t pcnt=0;
+			for (size_t i=0;i<n;i++){ strncpy(pool[pcnt], props[i].uci, 8); weights[pcnt++] = (int)(n - i); }
+			for (size_t i=0;i<lcnt;i++){
+				if (!uci_in_list(legal[i], pool, pcnt)) {
+					memcpy(pool[pcnt], legal[i], 8);
+					pool[pcnt][7] = '\0';
+					weights[pcnt++] = 1; total++;
+				}
+			}
+			// weighted pick
+			int wsum=0; for (size_t i=0;i<pcnt;i++) wsum += weights[i];
+			int r = (wsum>0)? (rand()%wsum) : 0;
+			size_t pick=0; for (size_t i=0;i<pcnt;i++){ if (r < weights[i]) { pick=i; break; } r -= weights[i]; }
+			// 5. play response
+			Move m; if (!parse_uci_move(pool[pick], &app.pos, &m)){ // fallback: best
+				if (n>0 && parse_uci_move(props[0].uci, &app.pos, &m)) pick=0; else { snprintf(status, sizeof(status), "No engine move"); quit=true; continue; }
+			}
+			chess_make_move(&app.pos, &m);
+			position_push_move_text(&app.pos, &m, line_uci, sizeof(line_uci));
+			awaiting_player = true;
+			// 6. Ask engine for optimal response from player
+			engine_get_best_move(&app.engine, &app.pos, expected_player_move);
+			snprintf(status, sizeof(status), "Your turn");
+			continue;
+		}
+
+		// Player move input
+		int key=0;
+		bool updated = gui_poll_move(&app.gui, &sel, &quit, &key);
+		if (quit) break;
+		if (key=='m' || key=='M'){
+			// enter simple replay: load a mistake line and restart from it to the position where best move is required
+			if (app.mistakes.count>0){
+				if (app.replay_index >= app.mistakes.count) app.replay_index = 0;
+				Mistake *mk = &app.mistakes.items[app.replay_index++];
+				// reset and play the line moves to reach the mistake position
+				chess_init_start(&app.pos);
+				char tmp[512]; snprintf(tmp, sizeof(tmp), "%s", mk->line);
+				char *tok = strtok(tmp, " ");
+				while (tok){ Move m; if (parse_uci_move(tok, &app.pos, &m)) chess_make_move(&app.pos, &m); tok = strtok(NULL, " "); }
+				snprintf(status, sizeof(status), "Practice: best is %s", mk->best_move);
+				strncpy(expected_player_move, mk->best_move, sizeof(expected_player_move));
+				awaiting_player = true;
+				gui_set_flipped(&app.gui, !app.pos.white_to_move); // if it's black to move, flip so black bottom
+			}
+		}
+		if (updated && sel.clicked && sel.to_sq>=0){
+			Move list[MAX_MOVES]; size_t n = chess_generate_legal_moves(&app.pos, list, MAX_MOVES);
+			bool moved=false; Move chosen={0};
+			for (size_t i=0;i<n;i++){
+				if (list[i].from==sel.from_sq && list[i].to==sel.to_sq){ chosen = list[i]; moved=true; break; }
+			}
+			sel.clicked=false; sel.from_sq=sel.to_sq=-1; sel.promo=0;
+			if (!moved) continue;
+
+			// 7. Compare with expected move
+			char uci[8]; move_to_uci(&chosen, uci);
+			bool correct = (expected_player_move[0] && strncmp(uci, expected_player_move, 8)==0);
+			if (correct){
+				chess_make_move(&app.pos, &chosen);
+				position_push_move_text(&app.pos, &chosen, line_uci, sizeof(line_uci));
+				snprintf(status, sizeof(status), "Correct");
+				awaiting_player = false; // engine move next
+			} else {
+				// log mistake: 1) save all moves that lead to mistake, 2) allow revisit later, 3) reset position
+				char fen[256]; chess_to_fen(&app.pos, fen, sizeof(fen));
+				mistakes_add(&app.mistakes, fen, expected_player_move, line_uci);
+				mistakes_save(&app.mistakes, mistake_file_path());
+				snprintf(status, sizeof(status), "Wrong, best was %s", expected_player_move);
+				// redo best move to show
+				Move best; if (parse_uci_move(expected_player_move, &app.pos, &best)){
+					chess_make_move(&app.pos, &best);
+					position_push_move_text(&app.pos, &best, line_uci, sizeof(line_uci));
+				}
+				gui_draw(&app.gui, app.pos.board, &sel, status);
+				SDL_Delay(600);
+				// reset to start
+				chess_init_start(&app.pos);
+				line_uci[0]='\0';
+				// randomize side again
+				player_is_white = rand()%2==0; gui_set_flipped(&app.gui, !player_is_white);
+				awaiting_player = player_is_white;
+				expected_player_move[0]='\0';
+			}
+		}
+
+		SDL_Delay(10);
+	}
+
+	mistakes_save(&app.mistakes, mistake_file_path());
+	gui_destroy(&app.gui);
+	engine_stop(&app.engine);
+	mistakes_free(&app.mistakes);
+	return 0;
+}
diff --git a/C/opening_learner/main.o b/C/opening_learner/main.o
new file mode 100644
index 0000000..e59782f
Binary files /dev/null and b/C/opening_learner/main.o differ
diff --git a/C/opening_learner/mistakes.c b/C/opening_learner/mistakes.c
new file mode 100644
index 0000000..89f76b0
--- /dev/null
+++ b/C/opening_learner/mistakes.c
@@ -0,0 +1,65 @@
+#include "mistakes.h"
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+
+void mistakes_init(MistakeList *ml) {
+    ml->items = NULL; ml->count = 0; ml->cap = 0;
+}
+
+void mistakes_free(MistakeList *ml) {
+    free(ml->items); ml->items = NULL; ml->count = ml->cap = 0;
+}
+
+static void ensure_cap(MistakeList *ml, size_t need) {
+    if (need <= ml->cap) return;
+    size_t ncap = ml->cap ? ml->cap*2 : 16;
+    while (ncap < need) ncap *= 2;
+    Mistake *ni = realloc(ml->items, ncap * sizeof(Mistake));
+    if (!ni) return; // OOM silently ignored
+    ml->items = ni; ml->cap = ncap;
+}
+
+void mistakes_add(MistakeList *ml, const char *fen, const char *best_move, const char *line) {
+    ensure_cap(ml, ml->count+1);
+    Mistake *m = &ml->items[ml->count++];
+    snprintf(m->fen, sizeof(m->fen), "%s", fen);
+    snprintf(m->best_move, sizeof(m->best_move), "%s", best_move);
+    snprintf(m->line, sizeof(m->line), "%s", line);
+}
+
+bool mistakes_save(const MistakeList *ml, const char *path) {
+    FILE *f = fopen(path, "w");
+    if (!f) return false;
+    for (size_t i=0;i<ml->count;i++) {
+        const Mistake *m = &ml->items[i];
+        fprintf(f, "FEN:%s\nBEST:%s\nLINE:%s\n.\n", m->fen, m->best_move, m->line);
+    }
+    fclose(f); return true;
+}
+
+bool mistakes_load(MistakeList *ml, const char *path) {
+    FILE *f = fopen(path, "r");
+    if (!f) return false;
+    char buf[1024]; char fen[128] = ""; char best[16] = ""; char line[512] = "";
+    while (fgets(buf, sizeof(buf), f)) {
+        if (strncmp(buf, "FEN:", 4) == 0) {
+            // copy up to 127 chars, strip newline
+            size_t l = strnlen(buf+4, sizeof(fen)-1);
+            memcpy(fen, buf+4, l); fen[l]='\0';
+            if (l && fen[l-1]=='\n') fen[l-1]='\0';
+        } else if (strncmp(buf, "BEST:", 5) == 0) {
+            size_t l = strnlen(buf+5, sizeof(best)-1);
+            memcpy(best, buf+5, l); best[l]='\0';
+            if (l && best[l-1]=='\n') best[l-1]='\0';
+        } else if (strncmp(buf, "LINE:", 5) == 0) {
+            size_t l = strnlen(buf+5, sizeof(line)-1);
+            memcpy(line, buf+5, l); line[l]='\0';
+            if (l && line[l-1]=='\n') line[l-1]='\0';
+        } else if (buf[0]=='.') {
+            mistakes_add(ml, fen, best, line);
+            fen[0]=best[0]=line[0]='\0';
+        }
+    }
+    fclose(f); return true;
+}
diff --git a/C/opening_learner/mistakes.h b/C/opening_learner/mistakes.h
new file mode 100644
index 0000000..7f77ce5
--- /dev/null
+++ b/C/opening_learner/mistakes.h
@@ -0,0 +1,28 @@
+#ifndef MISTAKES_H
+#define MISTAKES_H
+
+#include <stddef.h>
+#include <stdbool.h>
+
+// A lightweight mistake store in memory + file persistence.
+
+typedef struct {
+    char fen[128];
+    char best_move[8];
+    // PGN-like ply list in UCI for context
+    char line[512];
+} Mistake;
+
+typedef struct {
+    Mistake *items;
+    size_t count;
+    size_t cap;
+} MistakeList;
+
+void mistakes_init(MistakeList *ml);
+void mistakes_free(MistakeList *ml);
+void mistakes_add(MistakeList *ml, const char *fen, const char *best_move, const char *line);
+bool mistakes_save(const MistakeList *ml, const char *path);
+bool mistakes_load(MistakeList *ml, const char *path);
+
+#endif
diff --git a/C/opening_learner/mistakes.o b/C/opening_learner/mistakes.o
new file mode 100644
index 0000000..e8e7eba
Binary files /dev/null and b/C/opening_learner/mistakes.o differ
diff --git a/C/opening_learner/mistakes.txt b/C/opening_learner/mistakes.txt
new file mode 100644
index 0000000..3512742
--- /dev/null
+++ b/C/opening_learner/mistakes.txt
@@ -0,0 +1,12 @@
+FEN:rnbqkbnr/pppp1ppp/4p3/8/8/N4N2/PPPPPPPP/R1BQKB1R b KQkq - 1 2
+BEST:f8a3
+LINE:g1f3 e7e6 b1a3
+.
+FEN:rnbqkbnr/pppppppp/8/8/8/7P/PPPPPPP1/RNBQKBNR b KQkq - 0 1
+BEST:e7e5
+LINE:h2h3
+.
+FEN:rnbqkbnr/pppp1ppp/8/4p3/8/4P3/PPPPKPPP/RNBQ1BNR b kq - 1 2
+BEST:d7d5
+LINE:e2e3 e7e5 e1e2
+.
diff --git a/C/opening_learner/opening_learner b/C/opening_learner/opening_learner
new file mode 100755
index 0000000..578843f
Binary files /dev/null and b/C/opening_learner/opening_learner differ
diff --git a/C/opening_learner/run.sh b/C/opening_learner/run.sh
new file mode 100755
index 0000000..e88c54c
--- /dev/null
+++ b/C/opening_learner/run.sh
@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+set -euo pipefail
+cd "$(dirname "$0")"
+
+# Install SDL2 dev if sdl2-config is missing; otherwise build and run.
+
+if ! command -v sdl2-config >/dev/null 2>&1; then
+  echo "sdl2-config not found. Attempting to install SDL2 dev..."
+  if [ -f /etc/os-release ]; then
+    . /etc/os-release
+    case "$ID" in
+      ubuntu|debian|linuxmint|neon|pop)
+        sudo apt-get update
+        sudo apt-get install -y libsdl2-dev
+        ;;
+      arch|manjaro|endeavouros)
+        sudo pacman -Syu --noconfirm sdl2
+        ;;
+      fedora)
+        sudo dnf install -y SDL2-devel
+        ;;
+      opensuse*|sles)
+        sudo zypper install -y libSDL2-devel
+        ;;
+      void)
+        sudo xbps-install -Sy SDL2-devel
+        ;;
+      alpine)
+        sudo apk add sdl2-dev
+        ;;
+      *)
+        echo "Unsupported distro ($ID). Please install SDL2 dev manually and rerun." >&2
+        exit 3
+        ;;
+    esac
+  else
+    echo "/etc/os-release not found; cannot auto-detect distro. Install SDL2 dev manually." >&2
+    exit 3
+  fi
+fi
+
+./check_build.sh
+./opening_learner