如果用户输入非数字字符，如何仅扫描整数并重复读取? [英] How to scanf only integer and repeat reading if the user enters non-numeric characters?

问题描述

这里有一些C代码试图阻止用户键入字符或小于0或大于23的整数.

Here is some C code trying simply to prevent the user from typing a character or an integer less than 0 or more than 23.

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    const char *input;
    char *iPtr;
    int count = 0;
    int rows;

    printf("Enter an integer: ");
    scanf("%s", input);
    rows = strtol(input, &iPtr, 0);
    while( *iPtr != '\0') // Check if any character has been inserted
    {
        printf("Enter an integer between 1 and 23: ");
        scanf("%s", input);
    }
    while(0 < rows && rows < 24) // check if the user input is within the boundaries
    {
        printf("Select an integer from 1 to 23: ");
        scanf("%s", input);
    }  
    while (count != rows)  
    {  
        /* Do some stuff */  
    }  
    return 0;  
}

我完成了一半，将进行一次小小的俯卧撑.

I made it halfway through and a small push up will be appreciated.

推荐答案

使用 scanf(％d"，& rows)代替 scanf(％s"，input)

这使您可以直接从stdin获取整数值，而无需转换为int.

This allow you to get direcly the integer value from stdin without need to convert to int.

如果用户输入的字符串包含非数字字符，则必须在下一个 scanf(％d"，& rows)之前清除标准输入.

If the user enter a string containing a non numeric characters then you have to clean your stdin before the next scanf("%d",&rows).

您的代码可能看起来像这样:

your code could look like this:

#include <stdio.h>  
#include <stdlib.h> 

int clean_stdin()
{
    while (getchar()!='\n');
    return 1;
}

int main(void)  
{ 
    int rows =0;  
    char c;
    do
    {  
        printf("\nEnter an integer from 1 to 23: ");

    } while (((scanf("%d%c", &rows, &c)!=2 || c!='\n') && clean_stdin()) || rows<1 || rows>23);

    return 0;  
}

说明

1)

scanf("%d%c", &rows, &c)

这意味着期望用户输入一个整数，并在其附近输入一个非数字字符.

This means expecting from the user input an integer and close to it a non numeric character.

示例1: 如果用户输入 aaddk ，然后输入 ENTER ，则scanf将返回0.

Example1: If the user enter aaddk and then ENTER, the scanf will return 0. Nothing capted

Example2: :如果用户输入 45 ，然后输入 ENTER ，则scanf将返回2(2个元素带上限).在这里，％d 为 45 设置了标题，而％c 为 \ n

Example2: If the user enter 45 and then ENTER, the scanf will return 2 (2 elements are capted). Here %d is capting 45 and %c is capting \n

Example3: :如果用户输入 45aaadd ，然后输入 ENTER ，则scanf将返回2(2个元素带上限).在这里％d 为 45 设置了标题，而％c 为 a

Example3: If the user enter 45aaadd and then ENTER, the scanf will return 2 (2 elements are capted). Here %d is capting 45 and %c is capting a

2)

(scanf("%d%c", &rows, &c)!=2 || c!='\n')

在示例1中: 此条件为 TRUE ，因为scanf返回 0 (！= 2)

In the example1: this condition is TRUE because scanf return 0 (!=2)

在示例2中: 此条件为 FALSE ，因为scanf返回 2 和 c =='\ n'

In the example2: this condition is FALSE because scanf return 2 and c == '\n'

在示例3中: 此条件为 TRUE ，因为scanf返回 2 和 c =='a'(！='\ n')

In the example3: this condition is TRUE because scanf return 2 and c == 'a' (!='\n')

3)

((scanf("%d%c", &rows, &c)!=2 || c!='\n') && clean_stdin())

clean_stdin()始终为 TRUE ，因为该函数始终返回 1

clean_stdin() is always TRUE because the function return always 1

在示例1中: (scanf(％d％c"，& rows& c)！= 2 || c！='\ n')为 TRUE ，因此应检查&& 之后的条件，以便 clean_stdin()将被执行，整个条件为 TRUE

In the example1: The (scanf("%d%c", &rows, &c)!=2 || c!='\n') is TRUE so the condition after the && should be checked so the clean_stdin() will be executed and the whole condition is TRUE

在示例2中: (scanf(％d％c"，& rows& c)！= 2 || c！='\ n')为，因此不会检查&& 之后的条件(因为其结果是整个条件 FALSE )，因此将不会执行 clean_stdin()，整个条件为 FALSE

In the example2: The (scanf("%d%c", &rows, &c)!=2 || c!='\n') is FALSE so the condition after the && will not checked (because what ever its result is the whole condition will be FALSE ) so the clean_stdin() will not be executed and the whole condition is FALSE

在示例3中: (scanf(％d％c"，& rows& c)！= 2 || c！='\ n')为 TRUE ，因此应检查&& 之后的条件，以便 clean_stdin()将被执行，整个条件为 TRUE

In the example3: The (scanf("%d%c", &rows, &c)!=2 || c!='\n') is TRUE so the condition after the && should be checked so the clean_stdin() will be executed and the whole condition is TRUE

因此，您可以指出，只有当用户输入包含非数字字符的字符串时，才会执行 clean_stdin().

So you can remark that clean_stdin() will be executed only if the user enter a string containing non numeric character.

此条件((scanf(％d％c"，& rows& c)！= 2 || c！='\ n')&& clean_stdin())仅在用户输入 integer 且没有其他输入

And this condition ((scanf("%d%c", &rows, &c)!=2 || c!='\n') && clean_stdin()) will return FALSE only if the user enter an integer and nothing else

如果条件((scanf(％d％c"，& rows& c)！= 2 || c！='\ n')&& clean_stdin())是 FALSE ，而 integer 在 1 和 23 之间，然后是 while 循环将中断，否则 while 循环将继续

And if the condition ((scanf("%d%c", &rows, &c)!=2 || c!='\n') && clean_stdin()) is FALSE and the integer is between and 1 and 23 then the while loop will break else the while loop will continue

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