first write a program to catch all the prime numbers in to an array in a given or a chosen range....
and compare the elements of prime numbers with the each element of the array u want...
if one of ur array element is equal to a element of prime number array,,that means it's a prime number....

e.g.

A[4]={1,5,3,4,17}; //range is 1 to 20

primArray[10]={2,3,5,7,11,13,17,19}
now compare array 'A' with the each element of 'primArray'.

if u find hard to write a program to catch prime numbers of a given range to an array email me....

A prime number is a number that can only be evenly divided by itself and 1. Let number x equal a given element in the array. Now you can for loop from 2 to x-1 and use the modulus operator. If the resulting value is equal to 0 then it is certainly not a prime.

/* This program is for checking a single integer*/
#include<stdio.h>
#include<stdlib.h>
main()
{
int a,i;
printf("\nEnter a positive integer\n");
scanf("%d",&a);
if(a<=0)
{
printf("\nInvalid input\n");
exit(1);
}
for(i=2;i<=a-1;i++)
if(a%i==0)break;
if(i==a)printf("\n%d is prime\n",a);
else printf("\n%d is not a prime\n",a);
}
/* This is for elements in an array*/
#include<stdio.h>
#include<stdlib.h>
#define MAX 5
main()
{
int a[MAX],i,m;
printf("\nEnter elements into array\n");
for(m=0;m<=MAX-1;m++)
{
scanf("%d",&a[m]);
if(a[m]>0)
{
for(i=2;i<=a[m]-1;i++) if(a[m]%i==0)break;
if(i==a[m])printf("\n%d is prime\n",a[m]);
else printf("\n%d is not a prime\n",a[m]);
}
else printf("\n%d is not positive\n");
}
}

How can I make this to continue until the user presses N? I've tried using while(1), while( option == 'y' || option == 'Y') but it kept giving an error ...