检查用户输入长度（C 编程）

Question

我正在处理一个相当简单的问题，但我遇到了一个问题并且不确定为什么程序没有按照我想要的方式运行。该问题要求我们使用函数进行回文测试。我能够做到所有这些，但在问题中它还要求我们确保用户输入的是 5 位数字。这就是我在代码中所做的：

 do {
   printf("Please Enter a positive 5-digit number: "); //Ask & receive input
   scanf("%d", &number);
   countdigs = countDigits(number); //
   }while((countdigs != 5) && (number <0) );//keep going throught the loop while the number is less than 0 and is not equal to 5 digits    
 palindrome(number); //palindrome

这是我的回文函数

void palindrome (int number) //create palindrome procedure
{ 
 int remainder,reversedNumber=0,original; //initialize variables
 original = number; //set original number to a new var
 while (number != 0) //while the number is not 0
 {
  remainder = number %10; //get remainder of original number
  reversedNumber = (reversedNumber*10) + remainder; //construct reversed 
  number
  number = number / 10; //go to the next digit
 }
 //printf("OG = %d",original); //check
 //printf("rev = %d", reversedNumber); //check
 if (original == reversedNumber) //if the original number and reversed 
 number are the same
 {
  printf("The number %d is a palindrome.\n",original);  //print solution
 }
 else //if not the same
 {
  printf("The number %d is not a palindrome.\n",original); //print solution
 }
}

这是我的 countDigits 函数

int countDigits(int number) //setup recursive function
{
 int number_length=0; //initialize number length
 while(number != 0) //while the number is not 0
 {
  number = number/10; //divide number by 10 to get to next digit
  number_length = number_length + 1; //increase counter by 1
 }  
 return number_length; //return the counter
 printf("length %d",number_length);  
}

我遇到的问题是在这段代码中 (countdigs != 5) 这是检查以确保数字是正数（工作正常），并确保这个数字的长度是 5。但是，我无法让它工作。

问题说不要使用任何字符串函数（长度函数）

Answer 1

我猜问题出在最开始：

do {
    printf("Please Enter a positive 5-digit number: ");
    scanf("%d", &number);
    countdigs = countDigits(number);
} while((countdigs != 5) && (number < 0) );

如果 countdigs != 5 或 number 是否定的，我们应该再次要求用户输入，即：

do {
    printf("Please Enter a positive 5-digit number: ");
    scanf("%d", &number);
    countdigs = countDigits(number);
} while((countdigs != 5) || (number < 0) );

检查用户输入长度（C 编程）

Checking user input length (C programming)

c

user-input

input

palindrome