Question

我在程序中遇到字符验证问题。该程序无法使用isalpha（）。更确切地说，如果你输入一个字母而不是一个数字，它会进入一个无限循环...请帮忙。

#include <stdio.h>
#include <ctype.h>

#define TAB_SPACE_SIZE 8

int replaceTab(int numberOfTabs)
{
    int x;
    for (x = 0; x < numberOfTabs; x++)
    {
        char tabSpace[TAB_SPACE_SIZE];
        char space = ' ';
        int i;
          for (i = 0; i < 8; i++)
          {    
               tabSpace[i] = space;
               printf("%c", space);
          }
    }
}

int checkInput()
{
    int numberOfTabs;
    char response;
    char enter;
    printf("How many tabs am I to convert to spaces and print the output? ");
    scanf("%d", &numberOfTabs);
    if (numberOfTabs > 0)
    {
       replaceTab(numberOfTabs);
       system("pause");
       scanf("%c", &enter);
       printf("\nTry again? Yes(Y)/No(N)? ");
       scanf("%c", &response);
       printf("\n");
       switch (response)
       {
           case 'Y': checkInput();
                     break;
           case 'N': exit(0);
                     break;
           default: printf("\nEnter either Y or N.");
                    break;
       }
    }   
    else if (numberOfTabs == 0)
    {
       printf("The number of tabs cannot be zero. Press Enter to try again.");
       system("pause");
       checkInput();
    }
    else if isalpha(&numberOfTabs)
    {
       printf("You must enter a number. Press Enter to try again."); 
       system("pause");
       checkInput();
    } 
    else
    {
       printf("The number of tabs has to be a positive number. Press Enter to try again.");    
       system("pause");
       checkInput();                      
    }
    getchar();
    getchar();
}

int main()
{
    while (checkInput());
}

Answer 1

更改输入方案

...并删除未正确使用的isalpha(&numberOfTabs)

for (;;) {
  printf("How many tabs am I to convert to spaces and print the output? ");
  char buf[40];
  if (fgets(buf, sizeof buf, stdin) == NULL) {
    printf("We are done."); 
    return -1;
  }
  if (1 != sscanf(buf, &numberOfTabs)) {
    printf("You must enter a number. Try again."); 
    continue;
  }
  if (numberOfTabs <= 0) {
    printf("The number of tabs has to be a positive number. Try gain.");    
    continue;
  }
  else {
    break;  // I'd put this whole loop in a function and use return here.
  }
}

顺便说一句：在使用scanf("%c",的情况下，您希望scanf(" %c",使用前导空格。

Answer 2

你的其他if语句缺少paransheses，如果你在isalpha函数中得到numberOfTabs的地址，它会比较numberOfTabs 的地址是否为alpha。您可能希望将其更改为：

else if (isalpha(numberOfTabs))

关于下面的评论，您可以更改它，以便在scanf之后检查numberOfTabs是否为alpha：

scanf("%d", &numberOfTabs); if (numberOfTabs > 0 && !isalpha(numberOfTabs)) { ...

这样你的replaceTab函数中的循环不会循环x次（取决于你输入的字符）

C中的字符验证

2 个答案: