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Unit 6 Mastery Quiz: Loops & Iteration

I. Conceptual Questions​

1. Safety & Lifecycle: Why is it technically dangerous to use a standard while(true) loop instead of while(opModeIsActive()) in a LinearOpMode?

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opModeIsActive() monitors the Robot Controller's status. A while(true) loop ignores the "Stop" button on the Driver Station entirely — the loop will never exit, meaning the hardware receives commands even after the match has ended, which can cause mechanical damage or safety violations.

2. Parallel Execution: In a high-performance TeleOp, why is using the sleep() method considered poor engineering practice compared to getRuntime() comparisons?

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The sleep() method blocks the entire program thread. During the sleep period, the Robot Controller cannot read sensor data, update gamepad state, or send commands to other motors. Using getRuntime() comparisons inside the main loop checks the time condition each cycle without halting anything else.

3. Array Efficiency: When managing a four-motor drivetrain, why is a for..each loop technically superior to accessing each motor variable individually (e.g., motor1.setPower(0); motor2.setPower(0); ...)?

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A for..each loop ensures every motor in the collection receives the command with fewer lines of code, reducing the risk of accidentally omitting a motor or introducing an off-by-one index error. It also makes the code easier to scale — adding a fifth motor only requires adding it to the array, not inserting another manual line.

4. Floating-Point Precision: When implementing a non-blocking timer, why must the programmer use the >= or < comparison operator with getRuntime() instead of the == equality operator?

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The internal clock increments in sub-milliseconds. Because getRuntime() returns a double that advances continuously, the value will almost certainly never be exactly equal to a stored target. Using < creates a range condition that will reliably trigger when the window closes, rather than waiting for an exact match that may never occur.

5. State Machine Rationale: Why does the SDK provide the init_loop() method, and how does its iterative nature improve autonomous reliability compared to a static init()?

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init_loop() runs repeatedly after the driver presses "Init" but before "Play." This allows the robot to poll sensor readiness over time — for example, waiting for an IMU to finish calibrating or for a vision pipeline to lock onto a target. A static init() runs only once and cannot react to hardware that takes a variable amount of time to become ready.

II. Debug the Code​

The following code is intended to run an intake motor at full power for exactly 3 seconds after the match starts. Identify and fix the 2 errors.

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
import com.qualcomm.robotcore.eventloop.opmode.Autonomous;
import com.qualcomm.robotcore.hardware.DcMotor;

@Autonomous(name="Timed_Intake")
public class TimedIntake extends LinearOpMode {

    @Override
    public void runOpMode() {
        DcMotor intake = hardwareMap.get(DcMotor.class, "intake")
        waitForStart();

        double endTime = getRuntime() + 3.0;

        while (opModeIsActive() && getRuntime() == endTime) {
            intake.setPower(1.0);
        }

        intake.setPower(0);
    }
}
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Error 1 — Syntax Error: The hardwareMap.get() statement on the first line of runOpMode() is missing a semicolon (;). Java requires every statement to be terminated with a semicolon for the compiler to parse it correctly.

DcMotor intake = hardwareMap.get(DcMotor.class, "intake"); // ← semicolon added

Error 2 — Logic Error: The while loop condition uses == to compare the runtime against endTime. Because getRuntime() returns a continuously advancing double, it will almost never be exactly equal to the stored target value — the loop will exit immediately (or never enter) without running the motor. The condition must use < to create a window:

while (opModeIsActive() && getRuntime() < endTime) {
    intake.setPower(1.0);
}

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