Actionscript Cookbook

5.8. Simulating a Coin Flip

Problem

You want to simulate a coin flipping or other Boolean (true/false) event in which there is a 50% chance of either outcome.

Solution

Use the randRange( ) method to generate an integer that is either 0 or 1 and then correlate each possible answer with one of the desired results.

Discussion

You can use the randRange( ) method from Recipe 5.7 to generate a random integer in the specified range. To relate this result to an event that has two possible states, such as a coin flip (heads or tails) or a Boolean condition (true or false), treat each random integer as representing one of the possible states. By convention, programmers use 0 to represent one state (such as “off”) and 1 to represent the opposite state (such as “on”), although you can use 1 and 2 if you prefer.

For example, here is how you could simulate a coin flip:

#include "Math.as"

function coinFlip (  ) {
  flip = Math.randRange(0, 1);
  if (flip == 0) {
    return "heads";
  } else {
    return "tails";
  }
}

// Example usage:
trace ("The result of the coin flip was " + coinFlip(  ));

Here, we write a function that tests our coinFlip( ) routine to see if it is reasonably even-handed. Do you expect a perfect 50/50 distribution regardless of the number of coin flips? Test it and see.

#include "Math.as"

function testCoinFlip (numFlips) {
  // We'll count how many of each result occurs. Initialize them to 0.
  var heads = 0;
  var tails = 0;

  // Repeat the process numFlips times and keep tabs on the results. for (var ...