How do I check if a number is an ARMSTRONG number?

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/* Write a program to check if a given number is
Armstrong number or not. */

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

main()
{
    int *digit;
    int size, total , i;
    total =0;
    printf(" how many digit number you want to know? e.g: 4\n");
    scanf(" %d", size);
    digit =( int*) malloc(size *(sizeof(int)));

    for( i=0 ; i<size  ; i++)
    {
        printf(" \n enter a number digit by digit:\n");
        scanf(" %d", &digit[i]);
        digit[i] = pow(digit[i], size);
        total += digit[i];
    }
   
   if( digit == total)
   {
    printf(" Its an Armstrong number ! \n");
    printf(" the total is %d\n", total);
   }
   else
   {
       printf(" Its not an Armstrong number\n");
   }
    free(digit);
    return 0;
}

What I have tried:

I tried this but the pointer to the heap memory is wrong? the program doesn't even go to the loop. It terminates as I enter size

Posted 21-Sep-22 9:07am

Sharyar Javaid

Updated 21-Sep-22 18:48pm

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jeron1 21-Sep-22 15:46pm

You could try changing the scanf line to this.

scanf(" %d", &size);

Sharyar Javaid 21-Sep-22 17:33pm

thanks.Now it does the calculations(for total) as expected but the digit value C is giving me is not what I input. the total is correct though!

jeron1 21-Sep-22 17:40pm

if( digit == total)

You're comparing digit (which is a pointer) to total (which is an int).

2 solutions

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Patrice T · Answer 1 · 2022-09-21T15:00:00

Solution 1

C++

if( digit == total)

An array of digits do not make an integer.
Program for Armstrong Numbers - GeeksforGeeks[^]

Hint: a modulo (%) allow you to extract the unit digit from an integer.

C++

int Unit= 153 % 10;

Posted 21-Sep-22 15:00pm

Patrice T

Comments

CPallini 22-Sep-22 1:57am

5.

Patrice T 22-Sep-22 3:57am

Than you

OriginalGriff · Answer 2 · 2022-09-21T18:48:00

To add to what Patrice and jeron have - rightly - said: Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

C

int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

If you had tried using the debugger from the start, you would have spotted the first problem in moments instead of waiting an hour for jeron to point it out, and the second pretty immediately as well instead of several hours later. Get used to it: it is your best friend in development and can literally save you many hours of frustration and hair pulling!