Add Ex 18.1

Author: jsquared21

Diff for: Exercise_18/Exercise_18_01/Exercise_18_01.class

@@ -0,0 +1,30 @@
+/*********************************************************************************
+* (Factorial) Using the BigInteger class introduced in Section 10.9, you can     *
+* find the factorial for a large number (e.g., 100!). Implement the factorial    *
+* method using recursion. Write a program that prompts the user to enter an      *
+* integer and displays its factorial.                                            *
+*********************************************************************************/
+import java.util.Scanner;
+import java.math.*;
+
+public class Exercise_18_01 {
+	/** Main method */
+	public static void main(String[] args) {
+		// Create a Scanner
+		Scanner input = new Scanner(System.in);
+		System.out.print("Enter an integer: ");
+		String n = input.nextLine();
+
+		// Display factorial
+		System.out.println("Factorial of " + n + " is " 
+			+ factorial(new BigInteger(n)));
+	}
+
+	/** Retrun the factorial for the specified number */
+	public static BigInteger factorial(BigInteger n) {
+		if (n.equals(BigInteger.ZERO)) // Base case
+			return BigInteger.ONE; 
+		else // Recursive call
+			return n.multiply(factorial(n.subtract(BigInteger.ONE)));
+	}
+}