Compilare: user.cpp: In function ‘int main()’: user.cpp:124:22: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] sir [ cate + 1 ] = NULL ; ^ user.cpp:139:22: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] sir [ cate + 1 ] = NULL ; ^ user.cpp:105:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen( IN , "r" , stdin ) ; ^ user.cpp:106:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen( OUT , "w" , stdout ) ; ^ user.cpp:109:20: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets ( A + 1 ) ; ^ user.cpp:110:20: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets ( B + 1 ) ; ^ /tmp/cckcQYk8.o: In function `main': user.cpp:(.text.startup+0x56): warning: the `gets' function is dangerous and should not be used.