Question

以下更新

我需要测试输入是否为整数，如果是，则继续执行某些操作。

如果输入不是整数，我需要打印错误信息并退出。

我使用的方法是scanf将返回读取项目的数量，在我的情况下我希望它返回1.所以我测试scanf是否返回1，并执行我的其他代码。

但是，出于某种原因scanf没有返回1我遇到了无限循环

代码：

/*
 * Read in a number of values to read and then print the average
 * of those values.
 */

#include <stdio.h>
#include "tfdef.h"
#define DEBUGGING 1;

int main() {
    int expected;
    int count;
    double sum;
    int value;
    int flag;

    while (flag = scanf("%d", &expected) != EOF) {
#ifdef DEBUGGING
        printf("flag: %d  expected: %d\n", flag, expected);
#endif

        if (flag == 1) {
            sum = 0;
            for (count = 0; count < expected; count++) {
                scanf("%d", &value);
                sum += value;
            }
            printf("Average of %d values is %.2f\n",
                   count, count != 0 ? sum / count : 0.0);
        } else {
            printf("Error! Can't read number of expected values.\n");
        }
    }
}

更新

以下代码似乎有效，除了初始输入是数字后跟字母的情况。例如：

输入：eeee33333
印刷：Error! Can't read number of expected values.

输入：333eeee
印刷：Debug1 flag:1 expected: 333

代码

#include <stdio.h>
#include "tfdef.h"
#define DEBUGGING 1;

int main() {
    int expected;
    int count;
    double sum;
    int value;
    int flag;

    while (flag = scanf("%d", &expected)) {
#ifdef DEBUGGING
        printf("Debug1 flag: %d  expected: %d\n", flag, expected);
#endif
        if (flag == EOF) { 
#ifdef DEBUGGING
            printf("Debug2 flag: %d  expected: %d\n", flag, expected);
#endif
            return 0; 
        }
        while (getchar() != '\n');

        if (flag == 1) {
            sum = 0;
            for (count = 0; count < expected; count++) {
                scanf("%d", &value);
                sum += value;
            }
            printf("Average of %d values is %.2f\n",
                   count, count != 0 ? sum / count : 0.0);
        }
    }
    printf("Error! Can't read number of expected values.\n");
}

Answer 1

此问题的最佳解决方案是使用fgets()读取输入并使用sscanf()进行解析，但是获得无限循环的原因是：您的测试不正确：

while (flag = scanf("%d", &expected) != EOF)

flag收到scanf和EOF的返回值之间的比较结果......您可能想要写这个：

while ((flag = scanf("%d", &expected)) != EOF)

但是如果用户键入了无法解析为int的内容，则此类输入会在stdin缓冲区中徘徊，而scanf()会继续尝试解析它。

尝试这种方法：

#include <stdio.h>

int getnumber(int *valp) {
    char line[80];
    char last;

    while (fgets(line, sizeof line, stdin)) {
        flag = sscanf(line, "%d %c", &expected, &last);
        if (flag < 1) {
            printf("Input is not a number: %s", line);
            continue;
        }
        if (flag > 1) {
            printf("Extra characters after number input: %s", line);
            continue;
        }
        return 0;
    }
    return EOF;
}

int main(void) {
    int expected;
    int count;
    double sum;
    int value;

    while (getnumber(&expected) != EOF) {
        sum = 0;
        for (count = 0; count < expected; count++) {
            if (getnumber(&value) == EOF) {
                printf("Error! Can't read number of expected values.\n");
                break;
            }
            sum += value;
        }
        printf("Average of %d values is %.2f\n",
               count, count != 0 ? sum / count : 0.0);
    }
    return 0;
}

如果输入不是整数，则尝试避免无限循环

1 个答案: