# C++ Program to Check Armstrong Number

To understand this example, you should have the knowledge of the following C++ programming topics:

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

`abcd... = an + bn + cn + dn + ...`

In the case of an Armstrong number of 3 digits, the sum of cubes of each digit is equal to the number itself. For example, 153 is an Armstrong number because

`153 = 1*1*1 + 5*5*5 + 3*3*3 `

## Example: Check Armstrong Number of 3 Digits

``````#include <iostream>
using namespace std;

int main() {
int num, originalNum, remainder, result = 0;
cout << "Enter a three-digit integer: ";
cin >> num;
originalNum = num;

while (originalNum != 0) {
// remainder contains the last digit
remainder = originalNum % 10;

result += remainder * remainder * remainder;

// removing last digit from the orignal number
originalNum /= 10;
}

if (result == num)
cout << num << " is an Armstrong number.";
else
cout << num << " is not an Armstrong number.";

return 0;
}``````

Output

```Enter a positive integer: 371
371 is an Armstrong number.```

In the program, we iterate through the while loop until originalNum is 0.

In each iteration of the loop, the cube of the last digit of orignalNum is added to result.

``````remainder = originalNum % 10;
result += remainder * remainder * remainder;``````

And, the last digit is removed from the `orignalNum`.

When the loop ends, the sum of the individual digit's cube is stored in result.

## Example: Check Armstrong Number of n Digits

``````#include <cmath>
#include <iostream>

using namespace std;

int main() {
int num, originalNum, remainder, n = 0, result = 0, power;
cout << "Enter an integer: ";
cin >> num;

originalNum = num;

while (originalNum != 0) {
originalNum /= 10;
++n;
}
originalNum = num;

while (originalNum != 0) {
remainder = originalNum % 10;

// pow() returns a double value
// round() returns the equivalent int
power = round(pow(remainder, n));
result += power;
originalNum /= 10;
}

if (result == num)
cout << num << " is an Armstrong number.";
else
cout << num << " is not an Armstrong number.";
return 0;
}``````

Output

```Enter an integer: 1634
1634 is an Armstrong number.```

In this program, the number of digits of the entered number is calculated first and stored in n.

And, the pow() function computes the power of individual digits in each iteration of the `while` loop.

Also Read:

Challenge

Write a function to check if a number is an Armstrong number.

• Return `"It's an Armstrong Number"` if `num` is an Armstrong Number. Otherwise, return `"It's not an Armstrong Number"`.
• An Armstrong number of three digits is an integer such that the sum of the cubes of its digits is equal to the number itself. For example, 371 is an Armstrong number since `3 ^ 3 + 7 ^ 3 + 1 ^ 3 = 371`.
• For example, if `num = 371`, the output should be `"It's an Armstrong Number"`.
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