Prime numbers in C and is_prime

I'm writing a program to find all of the prime numbers contained within a user input n. I am having trouble with the is_prime function.

#include <stdio.h>
#include <math.h>

main() {
  int n;
  int k;

  // gets user input for length of string
  // and stores it as n
  printf("Enter the value of n:");
  scanf("%d", &n);

  for (k = 2; k <= n; k++) {
    if (is_Prime(k) == 1) {
      printf("Printing primes less than or equal to %d: /n %d, &n, &k");
    }
  }

I want the output to look like this, but I am not sure how to print the list without using different variables for each prime number.

Printing primes less than or equal to 30:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29.


    //here is the is_Prime function
    is_Prime (int n)
    {
    for(j = 2; j <= n/2; j++)
    {
    if(n%j != 0)
    {
    return 1;
    break;
    }
    }
    if(n%j == 0 )
    return 0;
    }   

I am not sure how to call the is_prime subroutine? Any help?