Control Structures

beginner40 min

Making Decisions with if/else

Control structures help your program make decisions and repeat actions based on conditions.

If/Else Statements:

int batteryLevel = 75;

if (batteryLevel > 80) {
    System.out.println("Battery level is good");
} else if (batteryLevel > 50) {
    System.out.println("Battery level is okay");
} else if (batteryLevel > 20) {
    System.out.println("Battery level is low");
} else {
    System.out.println("Battery critically low!");
}

Comparison Operators:

Common Operators:

== - Equal to
!= - Not equal to
> - Greater than
< - Less than
>= - Greater than or equal
<= - Less than or equal

Loops - For Loop:

// For loop - when you know how many times to repeat
for (int i = 1; i <= 5; i++) {
    System.out.println("Count: " + i);
}

// For loop with arrays
int[] motorPowers = {50, 75, 100, 25};
for (int i = 0; i < motorPowers.length; i++) {
    System.out.println("Motor " + i + " power: " + motorPowers[i]);
}

Loops - While Loop:

// While loop - repeat based on a condition
int attempts = 0;
boolean sensorDetected = false;

while (!sensorDetected && attempts < 10) {
    sensorDetected = checkSensor();
    attempts++;
    System.out.println("Attempt " + attempts);
}

Logical Operators:

Combining Conditions:

&& - AND (both conditions must be true)
|| - OR (at least one condition must be true)
! - NOT (reverses the condition)

Examples:

// AND example
if (batteryLevel > 20 && motorTemperature < 80) {
    robot.startDriving();
}

// OR example  
if (gamepad1.a || gamepad1.b) {
    robot.activateClaw();
}

Try It Yourself:

Exercise 1: Control Flow

An if/else chain that sets motor speed based on distance to target
A for loop that checks multiple sensors
A while loop that runs until a button is pressed
Combine conditions using logical operators

Write control structures for robot behavior:

An if/else chain that sets motor speed based on distance to target

                  public void setMotorSpeedByDistance(double distanceToTarget) {
    double motorSpeed;
    
    if (distanceToTarget > 50) {
        motorSpeed = 1.0;  // Full speed for far distances
        System.out.println("Far from target - full speed");
    } else if (distanceToTarget > 20) {
        motorSpeed = 0.6;  // Medium speed
        System.out.println("Medium distance - reduced speed");
    } else if (distanceToTarget > 5) {
        motorSpeed = 0.3;  // Slow speed for precision
        System.out.println("Close to target - slow speed");
    } else {
        motorSpeed = 0.0;  // Stop when very close
        System.out.println("At target - stopping");
    }
    
    setDriveMotors(motorSpeed);
}

A for loop that checks multiple sensors

                  public void checkAllSensors() {
    String[] sensorNames = {"colorSensor", "distanceSensor", "touchSensor", "gyroSensor"};
    boolean[] sensorStatus = new boolean[4];
    
    System.out.println("=== Sensor Check ===");
    
    for (int i = 0; i < sensorNames.length; i++) {
        // Simulate sensor check (replace with actual sensor code)
        sensorStatus[i] = Math.random() > 0.2; // 80% chance of working
        
        if (sensorStatus[i]) {
            System.out.println(sensorNames[i] + ": [OK] Working");
        } else {
            System.out.println(sensorNames[i] + ": [ERROR] Error");
        }
    }
}

A while loop that runs until a button is pressed

                  public void waitForButtonPress() {
    System.out.println("Waiting for button press to continue...");
    
    while (!gamepad1.a && !gamepad1.b) {
        // Keep checking for button press
        telemetry.addData("Status", "Press A or B to continue");
        telemetry.update();
        
        // Small delay to prevent excessive CPU usage
        try {
            Thread.sleep(50);
        } catch (InterruptedException e) {
            break;
        }
    }
    
    if (gamepad1.a) {
        System.out.println("Button A pressed - continuing");
    } else if (gamepad1.b) {
        System.out.println("Button B pressed - continuing");
    }
}

Combine conditions using logical operators

                  public void robotSafetyCheck() {
    double batteryLevel = 75;
    double motorTemp = 45;
    boolean emergencyStop = false;
    boolean sensorError = false;
    
    // AND operator - both conditions must be true
    if (batteryLevel > 20 && motorTemp < 80) {
        System.out.println("Robot ready to operate");
    }
    
    // OR operator - at least one condition must be true
    if (emergencyStop || sensorError || batteryLevel < 10) {
        System.out.println("[WARNING] STOPPING ROBOT - Safety issue detected");
        stopAllMotors();
    }
    
    // NOT operator - reverse the condition
    if (!emergencyStop && !sensorError) {
        System.out.println("All systems normal");
    }
    
    // Complex combination
    if ((batteryLevel > 50 && motorTemp < 70) || 
        (batteryLevel > 30 && motorTemp < 60)) {
        System.out.println("Safe to run autonomous mode");
    }
}