Display factorial of a number till user wishes.

//Program to display factorial of a number.
#include<iostream.h>
#include<conio.h>
fac(int);
void main()
{
    clrscr();
    int a;
    char z;
    do
    {
        cout<<"Enter a number: ";
        cin>>a;
        a=fac(a);
        cout<<"The factorial is: "<<a<<endl;
        cout<<"Do you wish to display another factorial? (y/n): ";
        cin>>z;
    }
    while(z=='y'||z=='Y');
}

fac(int a)
{
    int i,b;
    for(i=1,b=1;i<=a;i++)
    b=b*i;
    return b;
}