Compilare: user.cpp: In function ‘int main()’: user.cpp:41:28: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sub.in","r",stdin); ^ user.cpp:42:30: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sub.out","w",stdout); ^ user.cpp:43:18: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n",&n1); ^ user.cpp:45:14: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s+1); n=strlen(s+1); ^ /tmp/ccLeEh71.o: In function `main': user.cpp:(.text.startup+0x8d): warning: the `gets' function is dangerous and should not be used.