• Source 
    1. #include<stdio.h>
    2. int fact(int x);    //Function declaration
    3. main()
    4. {
    5.     	int x,ans;
    6.     	printf(" Enter the number : ");
    7.     	scanf("%d",&x);
    8.     	ans=fact(x);    //Function Call
    9.     	printf("\n The factorial of %d is : %d",x,ans);
    10.      return 0;
    11.  
    12. }    //Main function ends here
    13.  
    14. int fact(int x)    //Function Structure
    15. {
    16.     	int f;
    17.     	if(x==0)
    18.     	return 1;
    19.     	else
    20.     	f=x*fact(x-1);
    21.     	return f;
    22. }