Compilare: user.cpp: In function ‘int main()’: user.cpp:36:32: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[poz] = NULL; ^ user.cpp:48:32: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[poz] = NULL; ^ user.cpp:57:32: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[poz] = NULL; ^ user.cpp:66:32: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[poz] = NULL; ^ user.cpp:18:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("bool.in", "r", stdin); ^ user.cpp:19:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("bool.out", "w", stdout); ^ user.cpp:21:15: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(expr); ^ user.cpp:74:22: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n", &n); ^ user.cpp:75:15: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(expr); ^ /tmp/ccl5oqhF.o: In function `main': user.cpp:(.text.startup+0x5b): warning: the `gets' function is dangerous and should not be used.