help on loop

This is a discussion on help on loop within the C Programming forums, part of the General Programming Boards category; Because your while-loop is wrong. You need two loops, one to repeat the input of numbers and all the code ...

  1. #46
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    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.

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  2. #47
    C++ Witch laserlight's Avatar
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    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.
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  3. #48
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    Psh... I don't see what the problem was to my approach. And since I used 64-bit numbers you can even have reasonably long numbers before buffer overflows come out to play.

  4. #49
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    Thumbs up

    i have finaly make this program work the way i wanth.. thanks guys...

    this is the code that i have used..

    Code:
    #include <stdio.h>
    
    void main()
    {
    int a , b, c, d;
    int n;
    int temp;
    printf("Enter a five-digit number ( -1 to end ): \n");
    scanf("%d",&n);
    
    while(n!=-1)
    {
    a =n /10000;
    temp=n%10000;
    b =temp /1000;
    temp=n % 100;
    c=temp/10;
    temp=n%10;
    d =temp/1;
    if(a == d && b == c)
    {
    printf("%d is a palindrome\n" , n);
    printf("Enter a five-digit number ( -1 to end ): \n");
    scanf("%d",&n);
    }
    else
    {
    printf("%d is not a palindrome\n" , n);
    printf("Enter a five-digit number ( -1 to end ): \n");
    scanf("%d",&n);
    }
    }
    }

  5. #50
    and the hat of wrongness Salem's Avatar
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    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.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  6. #51
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    Thumbs up

    Quote Originally Posted by Salem View Post
    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.
    what?? dont get you.. i said i have made the program work the way i wan it..

  7. #52
    and the hat of wrongness Salem's Avatar
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    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.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  8. #53
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    Quote Originally Posted by StormRoBoT View Post
    i have finaly make this program work the way i wanth.. thanks guys...

    this is the code that i have used..

    Code:
    #include <stdio.h>
    
    void main()
    {
    int a , b, c, d;
    int n;
    int temp;
    printf("Enter a five-digit number ( -1 to end ): \n");
    scanf("&#37;d",&n);
    
    while(n!=-1)
    {
    a =n /10000;
    temp=n%10000;
    b =temp /1000;
    temp=n % 100;
    c=temp/10;
    temp=n%10;
    d =temp/1;
    if(a == d && b == c)
    {
    printf("%d is a palindrome\n" , n);
    printf("Enter a five-digit number ( -1 to end ): \n");
    scanf("%d",&n);
    }
    else
    {
    printf("%d is not a palindrome\n" , n);
    printf("Enter a five-digit number ( -1 to end ): \n");
    scanf("%d",&n);
    }
    }
    }
    int main (void)
    {
    int a, b, c, d;
    int n;
    int temp;

    do
    {
    printf("Enter a five-digit number < -1 to end >: ");
    scanf(" %d", &n); // if you are going to ask the user for input over and over again, it is always good to clear the input stream.

    a = n / 10000;
    temp = n % 10000;
    b = temp / 1000;
    temp = n % 100;
    c = temp/10;
    temp = n%10;
    d = temp/1;

    if(a == d && b == c)
    printf("%d is a palindrome\n", n);
    else
    printf("%d is not a palindrome\n" , n);

    while (n != -1); // as long as n is NOT -1, the loop continues.

    return 0;
    }

    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.

  9. #54
    CSharpener vart's Avatar
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    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
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