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In this tutorial, you will learn and get code about checking whether the given number by user (at run-time) is an Armstrong number or not. But before going through the program. Let's first understand about an Armstrong number.

For a number to be an Armstrong number, the sum of cubes of all of its digits must be equal to the number itself. For example, 153 is an Armstrong number. Because

- 153 = (1*1*1) + (5*5*5) + (3*3*3)

As you can clearly see that, the sum of cubes of all of its digit (1, 5, and 3) is equal to the number itself.
So it is an Armstrong number. But the number **26** is not an Armstrong number. Because

- 26 != (2*2*2) + (6*6*6)

Now let's move on and implement it in a C program.

The question is, **Write a program in C to check whether the given number is an Armstrong number or not**. The answer to this question is:

#include<stdio.h> #include<conio.h> int main() { int n, nu, num=0, rem; printf("Enter any positive number: "); scanf("%d", &n); nu=n; while(nu!=0) { rem = nu%10; num = num + (rem*rem*rem); nu = nu/10; } if(num==n) printf("\nIt's an Armstrong Number"); else printf("\nIt's not an Armstrong Number"); getch(); return 0; }

The above program was written under **Code::Blocks** IDE, therefore after successful build and run, here is the output you will get on your output screen:

Now supply any positive number say **153** and press ENTER key to see the output that will say whether it is an
Armstrong number or not as shown in the following snapshot:

- Get any positive number as input from user say
**153** - Now initialize the number to another variable say
**nu**for the operation - Include a while loop to work with each and every digit of the given number say
**153** - We have to find the remainder of the number one by one, the first remainder we will get is 3
- Initialize 3 to
**rem**variable and calculate cube of the**rem**and initialize it to**num**variable after summing it with the variable itself - We have initialize
**num**variable with 0 at starting of the program - Now divide the number
**nu**with 10 - And check whether the value inside
**nu**is not equal to 0 - If condition gets true, then again come inside the while loop
- And do the same operation until
**nu**holds the value 0 - Therefore at first run of the while loop,
**rem**holds**3**,**num**holds**0 + 3*3*3**or**27**and**nu**holds**15**. And at second run of while loop, rem holds 5, num holds**27 + 5*5*5**or**152**, and nu holds 1. And at third run, rem holds 1, num holds**152 + 1*1*1**or**153**, and nu holds 0 - At last check whether the value of
**num**is equal to the given number (the value present inside the variable**n**) or not - If it is equal, then the number is an Armstrong number, otherwise the number is not an Armstrong number

Here is another program in C, that prints all Armstrong number between any two given three-digit number. To generate or print Armstrong numbers without caring about digit, then refer to Generate Armstrong Numbers

#include<stdio.h> #include<conio.h> int main() { int n1, n2, i, temp, rem, sum, prod; printf("Enter the value of n1 (starting three-digit number): "); scanf("%d", &n1); printf("Enter the value of n2 (ending three-digit number): "); scanf("%d", &n2); printf("\n"); for(i=n1; i<=n2; i++) { sum = 0; temp = i; while(temp>0) { rem = temp%10; sum = sum + (rem*rem*rem); temp = temp/10; } if(sum == i) printf("%d is an Armstrong number.\n", i); } getch(); return 0; }

Here is the sample run:

Now provide any three-digit number as starting point, say **100** and another three-digit number as ending point
say **999** to print all the Armstrong numbers present in between these two numbers. Here is the second snapshot of the sample run:

Logic used in this program is almost same as used in the above one, except that we have used **for** loop here
to start it with **n1** (starting number) and ends with **n2** (ending number). In between these two numbers,
we have used the same concept inside the for loop, that is if the number is found as an Armstrong number, then print
it out, otherwise get to the next one to check for Armstrong.

Before check, initialize 0 to **sum**, and **i** to temp variable for the operation. Here we have used **sum**
variable in place of num variable. You can choose something different, it is up to you.

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