Compilare: user.cpp: In function ‘int main()’: user.cpp:30:26: warning: array subscript has type ‘char’ [-Wchar-subscripts] str[i] = C[str[i]]; ^ user.cpp:45:36: warning: array subscript has type ‘char’ [-Wchar-subscripts] ++cnt[index][str[j]]; ^ user.cpp:26:29: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d\n", &N, &M); ^ user.cpp:27:25: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%s", str + 1); ^ user.cpp:69:19: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(line); ^ /tmp/ccIegmUL.o: In function `main': user.cpp:(.text.startup+0x341): warning: the `gets' function is dangerous and should not be used.