Advanced Topics: Switch Statement

When implementing powerups in the case study game, the same ||sprites:Kind|| was used to maintain the same behavior for all the different powerups. The PowerUp type was kept seperate, and obtained using the powerUps.getType function, which took in a sprite and returned the type of power up that it represented.

This structure simplifed the behavior of the power ups - as they shared behavior outside of the bonus they gave the player - but required a long chain of ||logic:if ... else if|| checks in the event, with each ||logic:if condition|| simply checking the type returned by powerUps.getType against a different type of power up.

To more appropriately handle a situation like this, the switch statement can be used. This accepts a value, uses that value to select an appropriate case to run.

Concept: Switch-Case Syntax

The switch statement takes a value and checks that value against a series of cases. Combined, this is often called a switch case, as neither statement is particularly useful without the other.

switch (valueToCheck) {
    case FirstCase: {
        // code to run for FirstCase
        break;
    }
    case SecondCase: {
        // code to run for SecondCase
        break;
    }
    // repeat for as many cases as necessary
}

In this case, valueToCheck is the value that the switch case will match the case for: in the case study, this would be the type of the power up. FirstCase and SecondCase are two of the cases being checked: these would be two of the different PowerUpTypes, like PowerUpType.Health and PowerUpType.Score.

Example #1: What Number?

1. Review the code below
2. Identify which case will run
3. Identify how this would be written using ||logic:if|| and ||logic:else||

let myNumber: number = 2;
switch (myNumber) {
    case 1: {
        game.splash("My number is 1!");
        break;
    }
    case 2: {
        game.splash("My number is 2!");
        break;
    }
    case 3: {
        game.splash("My number is 3!");
        break;
    }
}

Student Task #1: Make the Switch

1. Start with the code below
2. Convert the ||logic:if ... else if|| section to use switch case

controller.A.onEvent(ControllerButtonEvent.Pressed, function () {
    info.changeScoreBy(1);
})

controller.B.onEvent(ControllerButtonEvent.Pressed, function () {
    if (info.score() == 0) {
        game.splash("You have no points!");
    } else if (info.score() == 1) {
        game.splash("You've got one point!");
    } else if (info.score() == 2) {
        game.splash("Two points!");
    }
})

Concept: Fall Through and Default Case

The break; statement at the end of each case is used to stop running the switch case, but is optional. Without it, the switch case will continue you “fall through” the cases until it reaches the end of the final case or a break statement. This can be used to handle multiple cases in the same way.

Additionally, a default case can be added, which will match any value. This can be thought of as an ||logic:else|| branch for the ||logic:if .. else if|| blocks.

Example #2: Using Fall Through and Default

1. Review the code below
2. Identify how the “fall through” is used to combine the cases for 1, 2, and 3
3. Identify how the “fall through” is used with cases 4 and 5
4. Identify how the default case is used for all other values

let myNumber: number = 2;
switch (myNumber) {
    case 1:
    case 2:
    case 3: {
        game.splash("My number is one, two, or three!");
        break;
    }
    case 4: {
        game.splash("My number is four, and the next number is");
    }
    case 5: {
        game.splash("five!");
        break;
    }
    default: {
        game.splash("My number is something else :(.")
    }
}

Student Task #2: More Options

1. Start with the code from task #1
2. Add cases for 3, 4, and 5. These should ||game:splash|| “My number is three, four, or five!”
3. Add a default case that will ||game:splash|| “That is a lot of points!”

Concept: Strings

Strings can also be used as values in the switch case.

Example #3: Switch Mystery

1. Review the code below, and copy it into a new project
2. Before running the code, identify what the expected output is for each of the three ||variables:mysteryInputs
3. Identify how the switch case is used to assign ||variables:output|| different values
4. Uncomment the first commented assignment of ||variables:mysteryInput|| and run the code. Check the code against your expected output from step 2
5. Repeat step 4 for the second and third assignments of ||variables:mysteryInput||

let output: string = "";
let mysteryInput = "";
// mysteryInput = "a";
// mysteryInput = "c";
// mysteryInput = "z";

switch (mysteryInput) {
    case "a": {
        output += "Hello! ";
    }
    case "b": {
        output += "I'm here!";
        break;
    }
    case "c": {
        output += "I'm actually here.";
        break;
    }
    default: {
        output += "Somewhere else";
    }
}

game.splash(output)

Student Task #3: How are You?

1. Start with the code snippet below
2. Convert the ||logic:if ... else if|| section to use switch case

let input: string = game.askForString("How are you?");

if (input == "good") {
    game.splash("That is good!");
} else if (input == "okay") {
    game.splash("Good enough!");
} else if (input == "bad") {
    game.splash("That's too bad!");
} else if (input == "I don't know" || input == "Something else") {
    game.splash("Okay.");
} else {
    game.splash("I don't understand.");
}