Compilare: main.cpp: In function 'void solve()': main.cpp:68:12: warning: unused variable 'mat' [-Wunused-variable] double mat[4] = {0, c - k, -k, -k}; ^~~ main.cpp: In function 'int main()': main.cpp:85:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("abcacm.in", "r", stdin); ^ main.cpp:86:39: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("abcacm.out", "w", stdout); ^