September Morn Update

Task/Factorial/Java/factorial-1.java

@@ -1,11 +1,53 @@
-public static long fact(final int n) {
-    if (n < 0) {
-        System.err.println("No negative numbers");
-        return 0;
+package programas;
+
+import java.math.BigInteger;
+import java.util.InputMismatchException;
+import java.util.Scanner;
+
+public class IterativeFactorial {
+
+  public BigInteger factorial(BigInteger n) {
+    if ( n == null ) {
+      throw new IllegalArgumentException();
     }
-    long ans = 1;
-    for (int i = 1; i <= n; i++) {
-        ans *= i;
+    else if ( n.signum() == - 1 ) {
+      // negative
+      throw new IllegalArgumentException("Argument must be a non-negative integer");
     }
-    return ans;
+    else {
+      BigInteger factorial = BigInteger.ONE;
+      for ( BigInteger i = BigInteger.ONE; i.compareTo(n) < 1; i = i.add(BigInteger.ONE) ) {
+        factorial = factorial.multiply(i);
+      }
+      return factorial;
+    }
+  }
+
+  public static void main(String[] args) {
+    Scanner scanner = new Scanner(System.in);
+    BigInteger number, result;
+    boolean error = false;
+    System.out.println("FACTORIAL OF A NUMBER");
+    do {
+      System.out.println("Enter a number:");
+      try {
+        number = scanner.nextBigInteger();
+        result = new IterativeFactorial().factorial(number);
+        error = false;
+        System.out.println("Factorial of " + number + ": " + result);
+      }
+      catch ( InputMismatchException e ) {
+        error = true;
+        scanner.nextLine();
+      }
+
+      catch ( IllegalArgumentException e ) {
+        error = true;
+        scanner.nextLine();
+      }
+    }
+    while ( error );
+    scanner.close();
+  }
+
 }