2017 SW Practical SET 1 Q5

#include <stdio.h>
#include <conio.h>
#include <ctype.h>

int isPrime(int);

int main(void)
{
    char choice;int ch, i, ctr;
    clrscr();
    do
    {
        ctr = 1;
        printf("\nPress 1 to print prime numbers\n");
        printf("Press 2 to print non-prime numbers\n");
        scanf("%d", &ch);
        switch(ch)
        {
            case 1: printf("The prime numbers are\n");
                for(i = 2; i <= 2000; i++)
                {
                    if(isPrime(i))
                    {
                        printf("%d,", i);
                        ctr++;
                    }
                    if((ctr%28) == 0)
                    {
                        printf("\nPress enter to see the next set of numbers....");
                        getch();
                        clrscr();
                        ctr = 1;
                        printf("\n\n");
                    }
                }
                break;
            case 2: printf("The non-prime numbers are\n");
                for(i = 2; i <= 2000; i++)
                {
                    if(!isPrime(i))
                    {
                        printf("%d,", i);
                        ctr++;
                    }
                    if((ctr%40) == 0)
                    {
                        printf("\nPress enter to see the next set of numbers....");
                        getch();
                        clrscr();
                        ctr = 1;
                        printf("\n\n");
                    }
                }
                break;
        }
        printf("\nDo you want to run again (Y/N)? ");
        choice = getche();
    }
    while(toupper(choice) == 'Y');
    getch();
    return 0;
}

int isPrime(int num)
{
    int limit = num/2;
    int ret = 1, i;
    for(i = 2; i <=limit; i++)
    {
        if((num%i) == 0)
        {
            ret = 0;
            break;
        }
    }
    return ret;
}