#include <stdio.h>

main
{
  int i,j,k,l=0;
	
	for i=2; i<=20; ++i
	{
	   for j=1; j<=i ; ++j
	   {
	     k = i%j;
	    
            if k == 0 
	    { l = ++l; 
	    }  
	    if l == 2
            {printf "%d is a prime \n",i
            }       
           }
        } 
	
	return 0;
}

#include <stdio.h>

int main(void)
{
	int i,j,l=0;
	
	while i <= 100
	{
	   l = 0;
	   
	   for j=1; j<=i; j++
	   {
	    if i%j == 0
	    {
	     l++;
	    }
	   
	   }
	   
	   if l == 2
	   {
	    printf "%d is a prime number\n" , i;
	   } 
	   
	   i++;
	}  
	
	return 0;
}

#include <stdio.h>

int main(void)
{
    int i=0,j=0,l=0;

    printf("1 is a prime number\n");
    printf("2 is a prime number\n");

    for (i=3; i < 101; i=i+2)
    {
        l = 0;

        // skip 1, don't go as high as i
        for (j=2; j<i; j++)
        {
            if (i % j == 0)
            {
                l++;
                // we already know it isn't prime
                break; 
            }
        }

        if (l == 0)
        {
            printf("%d is a prime number\n", i);
        }
    }

    return 0;
}