C Program To Find Armstrong Numbers Between Range using Function

In today’s video tutorial lets find all the Armstrong numbers or Narcissistic numbers between user entered range, using function / method.

An Armstrong number or Narcissistic number is an n-digit base b number such that the sum of its (base b) digits raised to the power n is the number itself.

Example 1:
If number = 370
It has 3 digits: 3, 7 and 0. So n = 3.
result = 3³ + 7³ + 0³ = 27 + 343 + 0 = 370.
So the original number 370 is equal to the result. So it’s an Armstrong Number.

Example 2:
If number = 8208
It has 4 digits: 8, 2, 0 and 8. So n = 4.
result = 8⁴ + 2⁴ + 0⁴ + 8⁴ = ‭4096‬ + 16 + 0 + ‭4096‬ = 8208.
So the original number 8208 is equal to the result. So it’s an Armstrong Number.

Related Read:
Swap 2 Numbers Using a Temporary Variable: C
Function / Methods In C Programming Language
C Program to Check Armstrong Number
C Program to print Armstrong Numbers Between Two Integers

Video Tutorial: C Program To Find Armstrong Numbers Between Range using Function

To count number of digits in a number

    int n = 0, temp;

    temp = num;

    while(temp)
    {
        temp = temp / 10;
        n++;
    }

To Iterate through the digits in the number

        while(num)
        {
            rem = num % 10;
            sum = sum + pow(rem, n);
            num = num / 10;
        }

To know above code logic, please visit and watch the video tutorial present at C Program to Check Armstrong Number.

Full Source Code: C Program To Find Armstrong Numbers Between Range using Function

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

float armstrong(int);

int main()
{
    int count, start, end, temp;

    printf("Enter start and end values\n");
    scanf("%d%d", &start, &end);

    if(start > end)
    {
        temp = start;
        start= end;
        end  = temp;
    }

    printf("Armstrong numbers between %d and %d are\n", start, end);

    for(count = start; count <= end; count++)
    {
        if(count == armstrong(count))
        {
            printf("%d is an Armstrong number\n", count);
        }
    }

    return 0;
}

float armstrong(int num)
{
    int rem, n = 0, temp;
    float sum = 0.0;

    temp = num;

    while(temp)
    {
        temp = temp / 10;
        n++;
    }

    while(num)
    {
        rem = num % 10;
        sum = sum + pow(rem, n);
        num = num / 10;
    }

    return(sum);
}

Output 1:
Enter start and end values
1
999
Armstrong numbers between 1 and 999 are
1 is an Armstrong number
2 is an Armstrong number
3 is an Armstrong number
4 is an Armstrong number
5 is an Armstrong number
6 is an Armstrong number
7 is an Armstrong number
8 is an Armstrong number
9 is an Armstrong number
153 is an Armstrong number
370 is an Armstrong number
371 is an Armstrong number
407 is an Armstrong number

Output 2:
Enter start and end values
500
99999
Armstrong numbers between 500 and 99999 are
1634 is an Armstrong number
8208 is an Armstrong number
9474 is an Armstrong number
54748 is an Armstrong number
92727 is an Armstrong number
93084 is an Armstrong number

Output 3:
Enter start and end values
1
99999
Armstrong numbers between 1 and 99999 are
1 is an Armstrong number
2 is an Armstrong number
3 is an Armstrong number
4 is an Armstrong number
5 is an Armstrong number
6 is an Armstrong number
7 is an Armstrong number
8 is an Armstrong number
9 is an Armstrong number
153 is an Armstrong number
370 is an Armstrong number
371 is an Armstrong number
407 is an Armstrong number
1634 is an Armstrong number
8208 is an Armstrong number
9474 is an Armstrong number
54748 is an Armstrong number
92727 is an Armstrong number
93084 is an Armstrong number

Output 4:
Enter start and end values
1
500
Armstrong numbers between 1 and 500 are
1 is an Armstrong number
2 is an Armstrong number
3 is an Armstrong number
4 is an Armstrong number
5 is an Armstrong number
6 is an Armstrong number
7 is an Armstrong number
8 is an Armstrong number
9 is an Armstrong number
153 is an Armstrong number
370 is an Armstrong number
371 is an Armstrong number
407 is an Armstrong number

Logic To Find Armstrong Numbers Between Range using Function

We ask the user to enter start and end value i.e., the range. Using for loop we iterate through all the numbers between start and end. For each iteration of for loop, variable count holds the number which we need to check if its Armstrong number or not.

Value of count is passed to function armstrong. Function armstrong counts the number of digits present in the integer number(we store it inside variable n) and then multiplies all the individual digits of the number by n and adds them. The sum is returned back to the calling function.

If value present in count and the value returned by armstrong method are equal, then the value present in count is an Armstrong number and will be displayed on the console window.

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