Display prime numbers upto n.

//Program to display prime numbers upto n.
#include<iostream.h>
#include<conio.h>
void main()
{
    clrscr();
    int a,b,c,z;
    cout<<"Enter a number: ";
    cin>>a;
    cout<<"The prime numbers upto "<<a<<" are: "<<endl;
    for(b=2;b<=a;b++)
    {
        z=0;
        for(c=1;c<=b;c++)
        {
            if(b%c==0)
            z++;
        }
        if(z==2)
        cout<<b<<" ";
    }
    getch();
}