Conditional Statements Lesson

Making Decisions in Code

Conditional statements are the brain of your program. They allow your robot to make decisions and execute different actions based on whether a certain condition is true or false, bringing intelligence and adaptability to its behavior.

The Power of Boolean Expressions

At the heart of every conditional statement is a boolean expression—a question that can only be answered with `true` or `false`. These expressions are built using the comparison and logical operators you've already learned. Your code will evaluate this expression and use the result to decide which path to take.

Example Boolean Expressions

Is the arm's angle greater than 90 degrees? (`armAngle > 90.0`)
Does the robot currently have a game piece? (`hasGamePiece == true`)
Is the shooter at speed AND is the turret aimed? (`shooterAtSpeed && turretAimed`)

The `if` Statement

The `if` statement is the most basic form of decision-making. It executes a block of code only if the specified condition is `true`. If the condition is `false`, the code block is skipped entirely.

// FRC Example: Only run the intake if the driver presses a button.
boolean intakeButtonPressed = true; // Assume this comes from a controller

if (intakeButtonPressed == true) {
    // This code will only run if the button is pressed.
    intakeMotor.set(0.8);
}

// The program continues from here regardless.

The `if-else` Statement

The `if-else` statement provides an alternative path. If the condition is `true`, the `if` block is executed. If the condition is `false`, the `else` block is executed. One of the two blocks is guaranteed to run.

// FRC Example: Checking if a game piece is detected.
boolean gamePieceSensorTripped = false;

if (gamePieceSensorTripped == true) {
    // Action if we have a piece
    intakeMotor.stop();
    indicatorLight.set(Color.Green);
} else {
    // Action if we DON'T have a piece
    intakeMotor.set(0.8);
    indicatorLight.set(Color.Red);
}

The `if-else if-else` Ladder

When you have multiple conditions to check in sequence, you use an `if-else if-else` ladder. The conditions are evaluated from top to bottom. As soon as one is found to be `true`, its code block is executed, and the rest of the ladder is skipped. The final `else` block is a catch-all that runs if none of the preceding conditions were true.

// FRC Example: Setting arm position based on driver input.
int desiredPosition = 2; // 1 for Intake, 2 for Amp, 3 for Stow

if (desiredPosition == 1) {
    arm.setAngle(110.0); // Go to intake position
} else if (desiredPosition == 2) {
    arm.setAngle(85.0); // Go to Amp scoring position
} else if (desiredPosition == 3) {
    arm.setAngle(0.0); // Go to stowed position
} else {
    // If an invalid number is given, do nothing or log an error.
    System.out.println("Invalid arm position requested!");
}

The `switch` Statement

A `switch` statement is a cleaner alternative to a long `if-else if-else` ladder when you are checking a single variable against multiple possible constant values. It can make your code more organized and easier to read.

// FRC Example: Choosing an autonomous routine.
String autoSelected = "Two Piece Center";

switch (autoSelected) {
    case "Two Piece Center":
        // Run the commands for this auto
        break; // The 'break' is crucial!

    case "Leave Community":
        // Run the commands for this auto
        break;

    default:
        // Run a default, safe auto if no match is found
        break;
}

Don't Forget `break;`

The `break;` statement is essential inside a `switch`. It tells the program to exit the `switch` block once a match is found. If you forget it, the code will "fall through" and execute the code for the next case as well, which is almost never what you want.

Test Your Knowledge

Question: You need to write code for a robot arm that has three distinct target positions: `INTAKE`, `SCORE`, and `CLIMB`. Which conditional structure would be the cleanest and most appropriate for choosing which angle to move the arm to?