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C++ Program to Check Armstrong Number



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In this article, you will learn and get code to check whether an input number is an armstrong number or not in C++. The program is created in these ways:

But before starting these programs, let's first understand about Armstrong number.

What is an Armstrong Number ?

A number that equals to the sum of its own digits, where each digit raised to the power of number of digits. For example, 1634 is an armstrong number, because:

1634 = 14 + 64 + 34 + 44
     = 1 + 1296 + 81 + 256
     = 1297 + 337
     = 1634

The result is equal to the number itself. So it is an Armstrong number.

Note - Because the total number of digit in 1634 is 4, so each of its digit raised to the power of 4.

Check Armstrong Number using while Loop

This is the first program of this article. It asks from user to enter a number and checks whether it is an Armstrong number or not.

The question is, write a program in C++ that checks whether a given number by user at run-time, is an Armstrong number or not. Here is its answer:

// C++ Check Armstrong Number using while Loop
// ----codescracker.com----

#include<iostream>
using namespace std;
int main()
{
    int num, temp, noOfDigit=0, res=0, rem, pow, i;
    cout<<"Enter the Number: ";
    cin>>num;
    temp = num;
    while(num>0)
    {
        num = num/10;
        noOfDigit++;
    }
    num = temp;
    while(num>0)
    {
        rem = num%10;
        pow = 1;
        i = 0;
        while(i<noOfDigit)
        {
            pow = pow*rem;
            i++;
        }
        res = res + pow;
        num = num/10;
    }
    if(res==temp)
        cout<<"\nIt is an Armstrong Number";
    else
        cout<<"\nIt is not an Armstrong Number";
    cout<<endl;
    return 0;
}

This program was build and run under Code::Blocks IDE. Here is its sample run:

C++ program find Armstrong number

Now supply any number say 1634 and press ENTER key to check whether it is an Armstrong number or not as shown in the snapshot given below:

C++ program check Armstrong number

And here is another sample run, with user input, 153:

check armstrong number c++

Note - Because 153 is a 3-digit number, therefore each digit will raised to the power of 3

The following block of code:

while(num>0)
{
    num = num/10;
    noOfDigit++;
}

is used to count total number of digits available in the given number.

The dry run of above program with user input, 153 goes like:

Check Armstrong Number using for Loop

Now let's create the same program as of previous one, using for loop. That is, this program does the same job as of previous program. The only difference is, in place of while loop, we've used for loop here:

// C++ Check Armstrong Number using for Loop
// ----codescracker.com----

#include<iostream>
using namespace std;
int main()
{
    int num, temp, noOfDigit=0, res=0, rem, pow, i;
    cout<<"Enter the Number: ";
    cin>>num;
    for(temp=num; temp>0; temp=temp/10)
        noOfDigit++;
    for(temp=num; temp>0; temp=temp/10)
    {
        rem = temp%10;
        pow = 1;
        for(i=0; i<noOfDigit; i++)
            pow = pow*rem;
        res = res + pow;
    }
    if(res==num)
        cout<<"\nIt is an Armstrong Number";
    else
        cout<<"\nIt is not an Armstrong Number";
    cout<<endl;
    return 0;
}

This program produces exactly the same output as of previous program. Here is its sample run with user input, 371:

check armstrong number using for loop c++

And here is the last sample run, with user input, 567:

c++ check armstrong number

Same Program in Other Languages

C++ Online Test


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