Compilare: user.c: In function ‘mergesort’: user.c:24: warning: statement with no effect user.c:29: warning: statement with no effect user.c: In function ‘main’: user.c:52: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result user.c:53: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result user.c:54: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result user.c:56: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result user.c:60: warning: control reaches end of non-void function