Compilare: user.cpp: In function ‘int main()’: user.cpp:137:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("treesmen.in", "r", stdin); ^ user.cpp:138:41: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("treesmen.out", "w", stdout); ^ user.cpp:142:22: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n", &N); ^ user.cpp:148:26: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] for(scanf("%d\n", &M); M; --M) ^ user.cpp:150:19: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(line); ^ user.cpp: In function ‘void read_input()’: user.cpp:121:15: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(line); ^ /tmp/cckkpy0c.o: In function `read_input()': user.cpp:(.text._Z10read_inputv[_Z10read_inputv]+0x1d): warning: the `gets' function is dangerous and should not be used.