重新提示用户，直到他/她输入大于1的正整数 [英] Re-prompting a user until he/she enters a positive integer value greater than 1

问题描述

我正在解决CS50（问题集1），即water.c。它要求用户编写一个程序，提示用户以分钟为单位的淋浴时间（以正整数表示），然后打印等量的水瓶（以整数表示）。
1分钟的淋浴=消耗了12瓶
主要问题：问题是我们必须确保用户输入的分钟数为正数，否则它将继续提示他返回输入/ scanf语句。只要他输入，他输入length <= 0，我就可以使用while（length <= 0）条件重新提示他，但是当他输入一个字符（即abc123）时，我的代码就会继续执行。任何解决方案？

I'm solving CS50 (problemset 1) i.e water.c. It asks user to write a program that prompts the user for the length of his or her shower in minutes (as a positive integer) and then prints the equivalent number of bottles of water (as an integer). 1 min of shower = 12 bottles consumed MAIN PROBLEM: The problem is that we have to ensure that the user inputs a positive number of minutes otherwise it keeps on re-prompting his back to input/scanf statement. As long as he enters he enters length<=0, I can re-prompt him back using while(length<=0) condition but as he enters a character i.e abc123 in input my code keeps on executing. Any solutions??

>

 #include <stdio.h>
 int main()
 {   int length=0;
    int min=12;
    int bottle=0;
    printf("Enter length of his or her shower in minutes");
    scanf("%d", &length);
    while (length <= 0){
    printf("Enter length of his or her shower in minutes");
    scanf("%d", &length);
    }
    bottle= (min*length);
    printf("%d", bottle);

    return 0;
 }

推荐答案

您可以通过阅读来解决首先是一个字符串，然后提取任何数字：

You can solve this by reading a string first, and then extracting any number:

#include <stdio.h>

int main(void)
{
    int length = 0;
    char input[100];
    while(length <= 0) {
        printf("Enter length: ");
        fflush(stdout);
        if(fgets(input, sizeof input, stdin) != NULL) {
            if(sscanf(input, "%d", &length) != 1) {
                length = 0;
            }
        }
    }

    printf("length = %d\n", length);
    return 0;
}

计划会议：

Enter length: 0
Enter length: -1
Enter length: abd3
Enter length: 4
length = 4

至关重要的是，我总是检查 scanf 的返回值，成功转换的项目数。

Crucially, I always check the return value from scanf, the number of items successfully converted.

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