ALGORITHM:  

    1. Start 

    2. Declare variables  

    3. Read the Input  number.

    4. Calculate sum of cubic of individual digits of the input. 

    5. Match the result with input number. 

    6. If match, Display the given number is Armstrong otherwise not. 

    7. Stop.

Program:

#include <stdio.h>
#include <math.h>
void main()
{
    int number, sum = 0, rem = 0, cube = 0, temp;
    printf ("enter a number:");
        scanf("%d", &number);
        temp = number;
        while (number != 0)
        {
            rem = number % 10;
            cube = pow(rem, 3);
            sum = sum + cube;
            number = number / 10;
        }
        if (sum == temp)
            printf ("The given number is armstrong number.");
        else
            printf ("The given number is not a armstrong number.");
    }

Output:

enter a number:370
The given number is armstrong number.