Compilare: main.cpp: In function 'void back(int, int, long long int)': main.cpp:31:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < v.size() ; ++i) ~~^~~~~~~~~~ main.cpp:36:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(k >= v.size() || Sum > S) return ; ~~^~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:46:39: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("spirala2.in", "r", stdin); ^ main.cpp:47:41: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("spirala2.out", "w", stdout); ^ main.cpp:49:26: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &n, &S); ^