Compilare: user.cpp: In function ‘int main()’: user.cpp:111:22: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] sir [ cate + 1 ] = NULL ; ^ user.cpp:126:22: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] sir [ cate + 1 ] = NULL ; ^ user.cpp:92:33: 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:93:35: 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:96:20: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets ( A + 1 ) ; ^ user.cpp:97:20: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets ( B + 1 ) ; ^ /tmp/ccFu2fkv.o: In function `main': user.cpp:(.text.startup+0x56): warning: the `gets' function is dangerous and should not be used.