Compilare: user.c: In function ‘quicksort’: user.c:34: warning: implicit declaration of function ‘rand’ user.c: In function ‘main’: user.c:62: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result user.c:63: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result user.c:65: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result user.c:68: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result