C program, using user-defined functions to check prime numbers or Armstrong numbers

Comprehensive Collection of C Programming Examples

In this example, you will learn to check if an integer is a prime number or an Armstrong (Armstrongnumber), or both.

To understand this example, you should understand the followingC programming languageTopic:

• C for loop

• C while and do ... while loops

• C break and continue statements

• C function

• Types of user-defined functions in C programming

In this program, create two user-defined functions checkPrimeNumber() and checkArmstrongNumber().

If the number entered by the user is a prime number, the checkPrimeNumber() function returns1. Similarly, if the number entered by the user is an Armstrong number, the checkArmstrongNumber() function will also return1.

Visit these pages to find out if there are numbers

• Check if there is a prime number

• Armstrong numbers

Example: Check Prime and Armstrong

#include <math.h>
#include <stdio.h>
int checkPrimeNumber(int n);
int checkArmstrongNumber(int n);
int main() {
　　　int n, flag;
　　　printf("Enter a positive integer: ");
　　　scanf("%d", &n);
　　　//Check prime number
　　　flag = checkPrimeNumber(n);
　　　if (flag ==　1)
　　　　　　printf("%d is a prime number.\n", n);
　　　else
　　　　　　printf("%d is not a prime number.\n", n);
　　　//Check Armstrong number
　　　flag = checkArmstrongNumber(n);
　　　if (flag ==　1)
　　　　　　printf("%d is an Armstrong number.", n);
　　　else
　　　　　　printf("%d is not an Armstrong number.", n);
　　　return 0;
}
//　Function to check prime number
int checkPrimeNumber(int n) {
　　　int i, flag =　1, squareRoot;
　　　//Calculate the square root
　　　squareRoot = sqrt(n);
　　　for (i =　2; i <= squareRoot;　++i) {
　　　　　　//Condition for non-prime number
　　　　　　if (n % i == 0) {
　　　　　　　　　flag = 0;
　　　　　　　　　break;
　　　　　　}
　　　}
　　　return flag;
}
//　Function to check Armstrong number
int checkArmstrongNumber(int num) {
　　　int originalNum, remainder, n = 0, flag;
　　　double result = 0.0;
　　　//　Store the number of digits of num in n
　　　for (originalNum = num; originalNum != 0;　++n) {
　　　　　　originalNum　/=　10;
　　　}
　　　for (originalNum = num; originalNum != 0; originalNum　/=　10) {
　　　　　　remainder = originalNum %　10;
　　　　　　//　The sum of the powers of each number stored in the result
　　　　　　result　+= pow(remainder, n);
　　　}
　　　//Armstrong Number Condition
　　　if (round(result) == num)
　　　　　　flag =　1;
　　　else
　　　　　　flag = 0;
　　　return flag;
}

Output Result

Enter a positive integer:　407
407　It is not a prime number.
407　It is an Armstrong number.

Comprehensive Collection of C Programming Examples