Compilare: user.cpp: In function ‘void update(int, int, int&)’: user.cpp:25:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < g[x1].size(); ++i) ^ user.cpp: In function ‘int main()’: user.cpp:59:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("substr.in", "r", stdin); ^ user.cpp:60:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("substr.out", "w", stdout); ^ user.cpp:63:29: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d\n", &n, &k); ^ user.cpp:64:16: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s + 1); ^ /tmp/ccO9bAHl.o: In function `main': user.cpp:(.text.startup+0x72): warning: the `gets' function is dangerous and should not be used.