Compilare: user.c: In function ‘quicksort’: user.c:34: warning: implicit declaration of function ‘rand’ user.c: In function ‘main’: user.c:59: warning: implicit declaration of function ‘srand’ user.c:59: warning: implicit declaration of function ‘time’ user.c:54: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result user.c:55: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result user.c:57: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result user.c:63: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result