Compilare: main.cpp: In function 'void backtrack()': main.cpp:36:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int ind = 0; ind < im.size(); ind++) { ~~~~^~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:78:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("immortal.in", "r", stdin); ^ main.cpp:79:39: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("immortal.out", "w", stdout); ^ main.cpp:82:30: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d%d", &n, &m, &k); ^ main.cpp:85:30: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &lin, &col); ^