/*
 *   Intro to Programming CSE 1310
 * University of Texas at Arlington
 */

package coderecursion26.ct17;

import java.util.Scanner;

/**
 *
 * @author jcmtiernan
 */
public class CodeRecursion26Ct17 
{

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) 
    {
        // calling a recursive method
        int testValue = 0;
        double testFac = 0;
        Scanner input = new Scanner(System.in);
        System.out.print("Please enter a positive integer value to take the factorial of: ");
        testValue = input.nextInt();
        testFac = fac(testValue);
        System.out.println("");
        System.out.println("The result of fac for "+testValue+" is "+testFac);
        
    }
    /**
     * Method fac - factorial function written recursively.
     * The function factorial can be generalized as shown below.
     * Method fac takes the generalization and implements it.

        0! = 1   // base case – stops the recursion

        1! = 0! * 1  // examples
        2! = 1! * 2
        3! = 2! * 3

        k! = (k – 1)! * k    // general (recursive) case – calls itself with different parameters

        To write a recursive function you must have:
                At least one base case, may have more than one base case
                At least one recursive case
                May also have an error case (or condition)

        Function header ( with access “static” return_type name (parameters)
        {
                test for the base case
                        return action for base case

                possible other tests
                        with other actions

                recursive call using return statement
        }
        public static int fac( int k )
        {
                if ( k == 0 )
                        return 1;
                return fac(k – 1) * k ;   
        }

        * @param k
     * @return 
     */
    public static int fac(int k)
    {
        if (k < 0)
            return 0;
        if (k == 0)
            return 1;
        System.out.println("in fac, k is "+k);
        return (fac(k-1) * k);
    }

}