C programming, Determine if a number is prime or an Armstrong number using a custom function.

#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);

   flag = checkPrimeNumber(n);

   if (flag == 1)

      printf("%d is a prime number.\n", n);

   else

      printf("%d is not a prime number.\n", n);

   flag = checkArmstrongNumber(n);

   if (flag == 1)

      printf("%d is an Armstrong number.", n);

   else

      printf("%d is not an Armstrong number.", n);

   return 0;

}

int checkPrimeNumber(int n) {

   int i, flag = 1, squareRoot;

   squareRoot = sqrt(n);

   for (i = 2; i <= squareRoot; ++i) {

      if (n % i == 0) {

         flag = 0;

         break;

      }

   }

   return flag;

}

int checkArmstrongNumber(int num) {

   int originalNum, remainder, n = 0, flag;

   double result = 0.0;

   for (originalNum = num; originalNum != 0; ++n) {

      originalNum /= 10;

   }

   for (originalNum = num; originalNum != 0; originalNum /= 10) {

      remainder = originalNum % 10;

      result += pow(remainder, n);

   }

   if (round(result) == num)

      flag = 1;

   else

      flag = 0;

   return flag;

}