scanf()接受到不满足条件时分成多种情况的处理

 printf("Enter days you want to live:");    item = scanf("%d", &days);    while (item != 1 || days < 0) {        if (days < 0) {            printf("Days must >= 0.\n");            printf("Enter days you want to live:");        }        if (item != 1) {            while ((c = getchar()) != '\n') {                if (EOF == c) {                    return EOF;                }                putchar(c);            }            printf(" is not valid num, try again.\n");            printf("Enter days you want to live:");        }        item = scanf("%d", &days);//scanf()只用一次    }