Compilare: user.c: In function ‘main’: user.c:38: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result user.c:39: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result user.c:40: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result user.c: In function ‘eval’: user.c:33: warning: control reaches end of non-void function