Thread: help on loop

Because your while-loop is wrong. You need two loops, one to repeat the input of numbers and all the code to check if the number is a palindrome and another one that covers the three lines that reverses the number. Currently, you are copying the last digit of a (or n) into b, but the remaining digits are still in a. You need to continue moving digits from a to b until there are no digits left in a.

--
Mats

What with including <iostream.h>? That's from pre-standard C++, and this is C. You got it right earlier by including <stdio.h>.

Take a good look at the code below:

Code:

#include <stdio.h>

int isPalindrome(int n);

int main()
{
    int n;

    printf("Enter a five-digit number ( -1 to end ): \n");
    scanf("&#37;d", &n);

    while (n != -1)
    {
        if (isPalindrome(n))
        {
            printf("%d is a palindrome\n", n);
        }
        else
        {
            printf("%d is not a palindrome\n", n);
        }

        printf("Enter a five-digit number ( -1 to end ): \n");
        scanf("%d", &n);
    }

    return 0;
}

/* Return 1 if n is a palindrome, else return 0. */
int isPalindrome(int n)
{
    /* ... */
}

It is basically your current code, except that it is well indented, includes the correct header, uses int main() instead of void main(), corrects the loop condition (you forgot to assign n to a, but with such undescriptive variable names, it is hard to know what is a and b anyway), shifts the duplicated code out of the if and else blocks, and... uses a function to determine if the number is a palindrome. Now you need to implement that function.

Right, so I have been pretty generous with the above, and I hope that at the very least in your future code you will indent your code properly and use descriptive names.

It's going to be a long road. 20 posts, and you're still using void main, and you still can't indent code at all.

You mean the way your current compiler lets you get away with.

Sooner or later, you'll change compiler. Only then will you discover that the slap-happy "works for me" approach was a folly. Been there, done that. If you want the T-shirt as well, then that's up to you.

Your code is already at the limits of understandability without any indentation. If it were 10 times longer, people would just ignore you.

I believe this code would do a better job than yours, you don't have to use scanf and printf over and over again. Just use a do while loop and set your condition to check whether n is NOT -1.

Use code tags for posting code

1. What will happen to your code if user enters string instead of number?
2. What will happen to your code if user enters 6-digit number?
3. etc