program to find prime number in a range c code example

Example 1: a c program to computes the prime numbers in the user mentioned range

#include <stdio.h>
int main()
{
   int num1, num2, flag_var, i, j;
 
   /* Ask user to input the from/to range
    * like 1 to 100, 10 to 1000 etc.
    */
   printf("Enter two range(input integer numbers only):");
   //Store the range in variables using scanf
   scanf("%d %d", &num1, &num2);
 
   //Display prime numbers for input range
   printf("Prime numbers from %d and %d are:\n", num1, num2);
   for(i=num1+1; i<num2; ++i)
   {
      flag_var=0;
      for(j=2; j<=i/2; ++j)
      {
         if(i%j==0)
         {
            flag_var=1;
            break;
         }
      }
      if(flag_var==0)
         printf("%d\n",i);
  }
  return 0;
}

Example 2: c program to check prime number using for loop

#include <stdio.h>
int main() {
    int n, i, flag = 0;
    printf("Enter a positive integer: ");
    scanf("%d", &n);

    for (i = 2; i <= n / 2; ++i) {

        // condition for non-prime
        if (n % i == 0) {
            flag = 1;
            break;
        }
    }

    if (n == 1) {
        printf("1 is neither prime nor composite.");
    }
    else {
        if (flag == 0)
            printf("%d is a prime number.", n);
        else
            printf("%d is not a prime number.", n);
    }

    return 0;
}