Compilare: user.cpp: In function ‘int expr(int, char*&)’: user.cpp:58: warning: unused variable ‘y’ user.cpp: In function ‘int main()’: user.cpp:75: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result user.cpp: In function ‘int eval(int, int, char)’: user.cpp:33: warning: control reaches end of non-void function