Decisions

The windshield wiper decision is a two-way decision (sometimes called a binary decision.) It seems small, but in programming complicated decisions are made of many small decisions. Here is a program that includes a binary decision.

import java.util.Scanner;

class NumberTester
{
  public static void main (String[] args) 
  {
    Scanner scan = new Scanner( System.in );
    int num;

    System.out.println("Enter an integer:");
    num = scan.nextInt();
    
    if ( num < 0 )   // is num less than zero?               
      System.out.println("The number " + num + " is negative");  // true branch
    else
      System.out.println("The number " + num + " is positive");  // false branch
    
    System.out.println("Good-bye for now");    // always executed
  }
}

The words if and else are markers that divide the decision into two sections. The else divides the true branch from the false branch. The if is followed by a question enclosed in parentheses. The expression num < 0 asks if the value in num is less than zero.

• The if statment always asks a question (often about a variable.)
• If the answer is true only the true-branch is exectued.
• If the answer is false only the false-branch is executed.
• No matter which branch is chosen, execution continues with the statement after the false-branch.

Notice that a two-way decision is like picking which of two roads to take to the same destination. The fork in the road is the if statement, and the two roads come together just after the false branch.