Tutorial Details:
Difficulty Level: Intermediate
Topics Covered: Using the Select statement to make decisions.
Assumed Knowledge: The Basics, My First Program, Constants and Variables, Conditionals (if)
Written By: BILL LANE

BACK

As we discussed in Conditional (If) it is very important to have a method to make decisions once our program is running. There is an excellent alternative to the if statement in the form of the select statement. Select is ideal when there are a number of possible options and is a lot neater than using nested if statements (that is if's inside if's inside if's). But it only works when you know exactly what the values will be. You can't use select to check if a value is greater than, or less than another value. So let's consider a situation where you would use select. Let's imagine you are building a mission that has a number of distinct stages. There may be a setup stage, a normal running stage, a I've been hit stage, a mission successful stage and a time up stage. You would typically assign a number to represent these different stages and have a variable to keep track of the current value. You could then use a select statement in your code to determine the current game state and respond in an appropriate manner. Let's see how this might work:

select gGameState{
  when 1 {sound 1}
  when 2 {sound 2}
  when 3 {sound 3}
  else {sound 4}
}

In this example, we start with the select keyword and then we have the name of the value we want to check. I'm checking on a global variable (hence the g at the start) gGameState. This is followed by an opening curly brace, with the closing curly brace encompassing a series of when statements.

The when statements are simple enough. The first when statement basically says that if gGameState equals 1 then play sound 1. The code checks each line and if it finds a match it executes the commands inside the curly braces. I've just used one command, but there can be multiple commands spanning many lines for each option. Note the else keyword after the last when. This works exactly the same as with the if statement and may be omitted if not required. If you don't include an else and none of the whens match then the program will continue on.

The select statement is very straight forward. But it's also incredibly useful. So keep it in mind when you need to make an important decision.