Example to check whether an integer (entered by the user) is an Armstrong number or not using while loop and if...else statement.

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

A positive integer is called an Armstrong number if the sum of cubes of individual digit is equal to that number itself. For example:

153 = 1 * 1 * 1 + 5 * 5 * 5 + 3 * 3 * 3 // 153 is an Armstrong number. 12 is not equal to 1 * 1 * 1 + 2 * 2 * 2 // 12 is not an Armstrong number.

```
#include <iostream>
using namespace std;
int main()
{
int origNum, num, rem, sum = 0;
cout << "Enter a positive integer: ";
cin >> origNum;
num = origNum;
while(num != 0)
{
rem = num % 10;
sum += rem * rem * rem;
num /= 10;
}
if(sum == origNum)
cout << origNum << " is an Armstrong number.";
else
cout << origNum << " is not an Armstrong number.";
return 0;
}
```

**Output**

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

In the above program, a positive integer is asked to enter by the user which is stored in the variable `origNum`.

Then, the number is copied to another variable `num`. This is done because we need to check the `origNum` at the end.

Inside the while loop, last digit is separated from `num` by the operation `digit = num % 10;`

. This digit is cubed and added to the variable `sum`.

Now, the last digit is discarded using the statement `num /= 10;`

.

In the next cycle of while loop, second last digit is separated, cubed and added to `sum`.

This continues until no digits are left in `num`. Now, the total sum `sum` is compared to the original number `origNum`.

If the numbers are equal, the entered number is an Armstrong number. If not, the number isn't an Armstrong number.