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C++ Program To Find Armstrong Numbers Between Two Integers

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A positive integer with digits a, b, c, d… is called an Armstrong number of order n if following condition is satisfied. 

abcd... = an + bn + cn + dn +...
153 = 1*1*1 + 5*5*5 + 3*3*3  
    =  1 + 125 + 27
    =  153        
Therefore, 153 is an Armstrong number.

Examples:

Input: 100 400
Output: 153 370 371
Explanation: 100 and 400 are given 
two integers.(interval)
  153 = 1*1*1 + 5*5*5 + 3*3*3 
      = 1 + 125 + 27
      =  153  
  370 = 3*3*3 + 7*7*7 + 0
      = 27 + 343 
      = 370
  371 = 3*3*3 + 7*7*7 + 1*1*1
      = 27 + 343 +1
      = 371

The approach implemented below is simple. We traverse through all numbers in given range. For every number, we first count number of digits in it. Let the number of digits in current number be n. Them we find sum of n-th power of all digits. If sum is equal to i, we print the number. 

C++




// C++ program to find Armstrong 
// numbers in a range
#include <bits/stdc++.h>
using namespace std;
  
// Prints Armstrong Numbers in a 
// given range
void findArmstrong(int low, int high)
{
    for (int i = low+1; i < high; ++i) 
    {
        // Number of digits calculation
        int x = i;
        int n = 0;
        while (x != 0) 
        {
            x /= 10;
            ++n;
        }
  
        // Compute sum of nth power of 
        // its digits
        int pow_sum = 0; 
        x = i;
        while (x != 0) 
        {
            int digit = x % 10;
            pow_sum += pow(digit, n);
            x /= 10;
        }
  
        // Checks if number i is equal 
        // to the sum of nth power of 
        // its digits
        if (pow_sum == i) 
            cout << i << " ";     
    }
}
  
// Driver code
int main()
{
    int num1 = 100;
    int num2 = 400;
    findArmstrong(num1, num2);
    cout << '';
    return 0;
}


Output:

153 370 371


Last Updated : 16 Jan, 2023
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