Compilare: user.cpp: In function ‘int main()’: user.cpp:75:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<sol.size();++i) ^ user.cpp:78:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<sol[i].size();++j) ^ user.cpp:79:49: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] cout<<sol[i][j]<<" \n"[j==sol[i].size()-1]; ^ user.cpp:53:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("johnie.in", "r", stdin); ^ user.cpp:54:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("johnie.out", "w", stdout); ^ user.cpp:57:27: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%i %i", &n, &m); ^ user.cpp:61:31: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%i %i", &a, &b); ^