//DISPLAY 4.16 Factorial Function
#include <iostream>
using namespace std;

//Function Declaration
int factorial(int n);
//Returns factorial of n.
//The argument n should be nonnegative.

int main ()
{
   int k;

   cout <<"Enter a natural number:";
   cin >> k;   

   cout <<"TRACING: calling factorial with argument " 
		  << "=" << k << endl;
   int result = factorial (k);
   cout <<"TRACING: After function call\n";

   cout <<"n="<< k
         <<"factorial of " << k 
        << " = " << result << endl;

   return 0;
}

//Function Definition
int factorial(int k)
{
   cout <<"TRACING: inside factorial, k=" 
        << k << endl;

    int product = 1;
    while (k > 0)
    {
        product = k * product;
        k--;
    }

    cout <<"TRACING: Before returning: "
         <<" k= " << k 
         <<" return " << product << endl; 
    return product;
}