Compilare: main.cpp: In function 'int main()': main.cpp:57:12: warning: converting to non-pointer type 'char' from NULL [-Wconversion-null] s[n--] = NULL; ^~~~ main.cpp:50:33: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("blis.in", "r", stdin); ^ main.cpp:51:35: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("blis.out", "w", stdout); ^ main.cpp:54:19: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d ", &k); ^ main.cpp:55:28: warning: ignoring return value of 'char* fgets(char*, int, FILE*)', declared with attribute warn_unused_result [-Wunused-result] fgets(s, NMAX + 5, stdin); ^