Armstrong Numbers from 1 to N using while and do-while loop

Introduction

In this tutorial, we will learn how to write a C program to print all Armstrong numbers from 1 to N using while and do-while loop.

An Armstrong number (also called a Narcissistic number or Pluperfect number) is a number that is equal to the sum of the cubes of its individual digits.

For example: 1, 153, 370, 371, and 407 are Armstrong numbers.

Example: 153 is an Armstrong number because:
1³ + 5³ + 3³ = 1 + 125 + 27 = 153

C Program using while loop

#include <stdio.h>

/* Write C Program to find all Armstrong numbers from 1 to N using while loop */

int main()
{
    int r = 0, limit, sum = 0, n = 1, n1;

    /* Input upper limit from user */
    printf("Enter upper limit to find Armstrong number: ");
    scanf("%d", &limit);

    printf("Armstrong numbers between 1 to %d are: \n", limit);

    while (n <= limit)
    {
        sum = 0;
        n1 = n;

        /* Calculate sum of cubes of digits */
        while (n1 != 0)
        {
            r = n1 % 10;
            sum += r * r * r;
            n1 = n1 / 10;
        }

        /* Check for Armstrong number */
        if (n == sum)
        {
            printf("%d, ", n);
        }
        n++;
    }

    return 0;
}

C Program using do-while loop

#include <stdio.h>

/* Write C Program to find all Armstrong numbers from 1 to N using do-while loop */

int main()
{
    int r = 0, limit, sum = 0, n = 1, n1;

    /* Input upper limit from user */
    printf("Enter upper limit to find Armstrong number: ");
    scanf("%d", &limit);

    printf("Armstrong numbers between 1 to %d are: \n", limit);

    do
    {
        sum = 0;
        n1 = n;

        /* Calculate sum of cubes of digits */
        do
        {
            r = n1 % 10;
            sum += r * r * r;
            n1 = n1 / 10;
        } while (n1 != 0);

        /* Check for Armstrong number */
        if (n == sum)
        {
            printf("%d, ", n);
        }
        n++;

    } while (n <= limit);

    return 0;
}

Sample Output

Enter upper limit to find Armstrong number: 407
Armstrong numbers between 1 to 407 are:
1, 153, 370, 371, 407

Another Example:

Enter upper limit to find Armstrong number: 1000
Armstrong numbers between 1 to 1000 are:
1, 153, 370, 371, 407

Program Explanation

Let's break down the code step by step using the while loop version:

1. Variable Declaration: int r=0, limit, sum=0, n=1, n1;
   • limit — stores the upper range
   • n — current number being checked
   • sum — stores the sum of cubes of digits
   • r — stores the remainder (individual digit)
   • n1 — temporary variable for processing
2. Input from User:
   printf("Enter upper limit to find Armstrong number: ");
scanf("%d", &limit);
   — The user enters a number (e.g., 407), which is stored in limit.
3. Outer while Loop: while(n <= limit)
   — This loop runs from 1 to limit. For each number, we check if it is an Armstrong number.
4. Calculate Sum of Cubes of Digits:
   — n1 = n; (copy the current number)
   — The inner while loop extracts each digit, calculates its cube, and adds it to sum.
   Example for 153:
   • Digit 3: r=3, sum=27, n1=15
   • Digit 5: r=5, sum=152, n1=1
   • Digit 1: r=1, sum=153, n1=0
5. Check Armstrong Condition:
   if(n == sum)
   — If the original number n equals the sum of cubes of its digits, it is an Armstrong number and gets printed.
6. Increment: n++;
   — Move to the next number and repeat until n > limit.
7. Return: return 0; — successful program execution.

Step-by-Step Approach

Algorithm to Find Armstrong Numbers

1. Start
2. Read the value of N (limit) from user
3. Initialize n = 1
4. While n <= N:
   • Set sum = 0
   • Set n1 = n
   • While n1 != 0:
     • r = n1 % 10
     • sum += r * r * r
     • n1 = n1 / 10
   • If n == sum, print n
   • n++
5. End

#include <stdio.h>
int main() {
    int num, r, sum;
    printf("3-digit Armstrong numbers are:\n");
    for(num = 100; num <= 999; num++) {
        sum = 0;
        int temp = num;
        while(temp != 0) {
            r = temp % 10;
            sum += r * r * r;
            temp = temp / 10;
        }
        if(num == sum)
            printf("%d, ", num);
    }
    return 0;
}

#include <stdio.h>
int main() {
    int num, r, sum = 0, temp;
    printf("Enter a number: ");
    scanf("%d", &num);
    temp = num;
    while(temp != 0) {
        r = temp % 10;
        sum += r * r * r;
        temp = temp / 10;
    }
    if(num == sum)
        printf("%d is an Armstrong number.\n", num);
    else
        printf("%d is NOT an Armstrong number.\n", num);
    return 0;
}

Frequently Asked Questions

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