Calculate Factorial in C

#include<stdio.h>

#include<conio.h>

void main()

{

long int multiply,num;

long int i=0,a,value,sum;

clrscr();

printf("enter number which you find the factorial =");

scanf("%ld",& num);

multiply=num;

value=num;

a=num-1;

while(i++<a)

{

    sum=value-i;

    multiply=multiply*sum;

}

printf("%ld",multiply);

getche();

}