How does a C program to display prime numbers between intervals using function work?

Courtesy: Programiz.com


1. In this program, we print all the prime numbers between n1 and n2. If n1 is greater than n2, we swap their values:

if (n1 > n2) {
  n1 = n1 + n2;
  n2 = n1 - n2;
  n1 = n1 - n2;
}

2. Then, we run a for loop from i = n1 + 1 to i = n2 - 1.

In each iteration of the loop, we check if i is a prime number using the checkPrimeNumber() function.

If i is prime, we print it.

for (i = n1 + 1; i < n2; ++i) {
  flag = checkPrimeNumber(i);
  if (flag == 1)
    printf("%d ", i);
  }
}

3. The checkPrimeNumber() function contains the code to check whether a number is prime or not.

int checkPrimeNumber(int n) {
  int j, flag = 1;
  for (j = 2; j <= n / 2; ++j) {
    if (n % j == 0) {
      flag = 0;
      break;
    }
  }
  return flag;
}

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