/* Homework 10(a): The program below computes the factorial of an integer using pointers.
Please read the comments provided below to understand better.
 */
#include<iostream>
#include <cmath>
using namespace std ;

/*
int factorial ( int num ) 

//here we are providing the value of the integer num. 
//Function is called by value for example factorial(4) 

{
  int i =1, fact;
  //fact =i ;

  while(i <= num)
    {
	
 // cout << "Iteration number " << i << endl;
	if (i ==1)
         {  fact = 1 ; //initialization
	// cout << "We are on iteration number = "<< i << endl; 
 	}
	
      fact=fact*i;
      i++;
    }

 return fact ;	
 
}

*/


void factorial (  int *num ) 
//here we are providing the a pointer num to the integer *num which is called by pointer num.

{
  int i =1;
  int temp =*num; //we need to temporarily store the number *num whose factorial we seek.
 
 //cout << "Num whose factorial we seek: "<< *num <<endl;	
  while(i < temp)
    {
  //cout << "Output before  = " << *num << endl;
   *num=(*num)*i;
   
  //cout << "Output after  = " << *num << endl;
   i++; 
    } //while loop
	
} 


int main()
{

  cout <<"**********Demonstrate the use calling function through reference**********" << endl ;
   int x;
  //declaring a pointer to an int. 
   int *num ;  //This pointer could be pointing to ANY integer.
   num = &x ;  //The pointer num now points to the integer x.
    
 /* //Note: ALTERNATE DECLARATIONS FOR POINTER:
   int * num ;
   int*  num ; 
 */

  
  //Input the number and save it.
  cout<<"Enter the no: ";
  cin>> x;
 

  //Calculate the factorial using loop
  cout << "calculating the factorial of "<< x << endl;
   factorial(num);  
// recall, num here is a pointer and this is what we mean by calling a function
// by reference we are pointing to the address instead of introducing a new variable fact 
// where we will store a variable, we just replace at the address of x, the value of its
// factorial.

    cout << "the factorial is "<< *num <<endl;
  return 0;
}