Before going to the program first let us understand what is a *Armstrong Number?*

**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.

In other word **“***A number is Armstrong if it is equal the sum of cube of its digits***.”**

For example,

153 is an *Armstrong number* because 1^{3} + 5^{3} + 3^{3} = 1 + 125 + 27 = 153

124 is not an *Armstrong number because *1^{3} + 2^{3} + 4^{3}= 1 + 8 + 64 = 73

## Program code for Armstrong Number or Not in C:

#include<stdio.h> #include<conio.h> void main() { int n,num,r,ans=0; clrscr(); printf("Enter a positive integer: "); scanf("%d", &num); n=num; /* Loop to calculate the sum of the cubes of its digits */ while(n>0) { r=n%10; ans=ans+r*r*r; n=n/10; } /* if else condition to print Armstrong or Not */ if(ans==num) printf("%d is an Armstrong number.",num); else printf("%d is not an Armstrong number.",num); getch(); }

## Working:

- First the computer reads the positive integer value from the user.
- Then using while loop it calculates the sum of the cubes of its digits.
- Finally if else condition is used to print the number is Armstrong or Not .

## Step by Step working of the above Program Code:

**For Armstrong Number:**

- Let us assume that a user enters the positive integer value as 153.
- It assigns the value of ans=0, num=153.
- It assigns the value of n=num(ie. n=153) and the loop continues till the condition of the while loop is true.

3.1. n>0 (153>0) while loop condition is true

r=n%10 (r=153%10) So r=3

ans=ans+r*r*r (ans=0+3*3*3) So ans=27

n=n/10 (n=153/10) So n=15

3.2. n>0 (15>0) while loop condition is true

r=n%10 (r=15%10) So r=5

ans=ans+r*r*r (ans=27+5*5*5) So ans=152

n=n/10 (n=15/10) So n=1

3.3. n>0 (1>0) while loop condition is true

r=n%10 (r=1%10) So r=1

ans=ans+r*r*r (ans=152+1*1*1) So ans=153

n=n/10 (n=1/10) So n=0

3.4. n>0 (0>0) while loop condition is false

It comes out of the while loop and checks whether the number is Armstrong or not.

- ans==num (153==153) if condition is true

It prints 153 is an Armstrong number.

- Thus program execution is completed.

**For Not an Armstrong Number:**

- Let us assume that a user enters the positive integer value as 431.
- It assigns the value of ans=0, num=431.
- It assigns the value of n=num(ie. n=431) and the loop continues till the condition of the while loop is true.

3.1. n>0 (431>0) while loop condition is true

r=n%10 (r=431%10) So r=1

ans=ans+r*r*r (ans=0+1*1*1) So ans=1

n=n/10 (n=431/10) So n=43

3.2. n>0 (43>0) while loop condition is true

r=n%10 (r=43%10) So r=3

ans=ans+r*r*r (ans=1+3*3*3) So ans=28

n=n/10 (n=43/10) So n=4

3.3. n>0 (4>0) while loop condition is true

r=n%10 (r=4%10) So r=4

ans=ans+r*r*r (ans=28+4*4*4) So ans=92

n=n/10 (n=4/10) So n=0

3.4. n>0 (0>0) while loop condition is false

It comes out of the while loop and checks whether the number is Armstrong or not.

- ans==num (92==431) if condition is true

It prints 431 is not an Armstrong number.

- Thus program execution is completed.