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 switch statement. switch 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 switch to check if a value is greater than, or less than another value. So let's consider a situation where you would use switch. 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 switch statement in your code to determine the current game state and respond in an appropriate manner. Let's see how this might work:

switch (gGameState)
{
  case 1: PlaySound(1); break;
  case 2: PlaySound(2); break;
  case 3: PlaySound(3); break;
  default: PlaySound(4); break;
}

In this example, we start with the switch keyword and then we have the name of the value we want to check in brackets. 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 case statements.

The case statements are simple enough. The first case 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. I've just used one command, but there can be multiple commands spanning many lines for each option. Note the break keyword at the end of each command. This tells the program to break out of (not continue checking) the rest of the cases. Also note the default keyword after the last case. It tells the program that if nothing else matches then it must use this command. It is optional and so may be omitted. If you don't include a default and none of the cases match then the program will continue on.

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