C Program to Find Armstrong Numbers Between Two Integers

Prerequisite: Program for Armstrong Numbers

A positive integer of n digits is called Armstrong number of order n (order is the number of digits) if 

abcd… = pow(a,n) + pow(b,n) + pow(c,n) + pow(d,n) + …. 

Here, we will build a C Program to print Armstrong Numbers between two integers. 

Example:

153 is an Armstrong number

1*1*1 + 5*5*5 + 3*3*3 = 153
 
370 is an Armstrong Number

3*3*3 + 7*7*7 + 0*0*0 = 370 

Input:

lowerlimit = 100 
higherlimit = 400 

Output: 

153 370 371

Below is the program to print all Armstrong numbers between the lower limit and the upper limit provided by the user.

C

// C Program to Demonstrate
// Armstrong numbers between
// two integers
#include <math.h>
#include <stdio.h>

int power(int x, unsigned int y)
{
    // Initialize result
    int res = 1;

    while (y > 0) {
        // If y is odd, multiply
        // x with result
        if (y & 1)
            res = res * x;

        // y must be even now
        y = y >> 1; // y = y/2
        x = x * x; // Change x to x^2
    }
    return res;
}

int main()
{
    int lowerlimit, higherlimit;
    printf("Enter lowerlimit and Higher limit:\n ");
    scanf("%d%d", &lowerlimit, &higherlimit);

    for (int i = lowerlimit + 1; i < higherlimit; ++i) {
        int x = i;
        int n = 0;

        // number of digits calculation
        while (x != 0) {
            x /= 10;
            ++n;
        }
        int powersum = 0;
        x = i;
        // finding the sum of n
        // th power of its digits
        while (x != 0) {
            int digit = x % 10;
            powersum += power(digit, n);
            x /= 10;
        }
        // checking if the obtained
        // number is armstrong or
        // not
        if (powersum == i)

            // printing the result
            printf("%d ", i);
    }
    printf("\n");
    return 0;
}

Output:

Enter lowerlimit and Higher limit: 100 400
153 370 371

Time Complexity: The time complexity of the program is O((n-m) * d * log(p)) where n and m are the given lower and upper limits respectively, d is the number of digits in the largest number in the range and p is the number of digits in the base of the number system (10 in this case).

Space Complexity: The space complexity of the program is O(1) as it uses only a constant amount of extra space regardless of the input size.