If / Else & First Sensor

Make the robot react. Drive until something happens.

The if pattern

if (DistanceSensor.objectDistance(mm) < 100) {
  LeftMotor.stop();
  RightMotor.stop();
} else {
  LeftMotor.spin(forward, 50, percent);
  RightMotor.spin(forward, 50, percent);
}

Read it like a sentence: "If the distance to the closest object is less than 100 mm, stop both motors. Otherwise, drive forward."

Drive until the bumper hits

One last reminder before we stop calling it out: the motors and the bumper are added by the Robot Configuration menu, and vexcodeInit() is auto-inserted at the top of main. From the next lesson on, we'll show only the part you actually write yourself.

int main() {
  vexcodeInit();   // VEXcode IQ adds this for you, leave it alone

  LeftMotor.spin(forward, 50, percent);
  RightMotor.spin(forward, 50, percent);

  // Loop until the bumper is pressed
  while (FrontBumper.pressing() == false) {
    wait(20, msec);  // small wait so we don't hog the CPU
  }

  LeftMotor.stop();
  RightMotor.stop();
}

Logical operators

You can combine conditions with && (and) and || (or).

if (FrontBumper.pressing() || DistanceSensor.objectDistance(mm) < 50) {
  // stop if either the bumper is pressed OR the wall is close
  LeftMotor.stop();
  RightMotor.stop();
}

Try it

Write a program that drives forward until a bumper is pressed, then backs up for 0.5 seconds, then stops. Two if-statements (or one while loop and one wait) is enough.

Curated references

• videoBasic Autonomous Programming with VEXcode IQ
• docsVEX IQ Full Volume: Autonomous Coding Skills

bool isPressed = FrontBumper.pressing();

if (isPressed = true) {
  LeftMotor.stop();
  RightMotor.stop();
}

LeftMotor.spin(forward, 50, percent);
RightMotor.spin(forward, 50, percent);

while (DistanceSensor.objectDistance(mm) < 100) {
  wait(20, msec);
}

LeftMotor.stop();
RightMotor.stop();