Control

Introduction

Control includes methods for timing, program flow, conditional logic, and project termination. These controls let you pause execution, create loops, define logic paths, and end a program.

Below is a list of available controls, including methods and C++ keywords:

• wait – Pauses execution for a given number of milliseconds or seconds.

• for – Repeats code for each item in a sequence.

• if – Executes code if a condition is true.

• if/else – Runs different code depending on a condition.

• if/else if/else – Checks multiple conditions in order.

• while – Repeats code while a condition is true.

• break – Exits a loop immediately.

• programStop – Ends the running program.

wait

wait pauses for a specific amount of time before moving to the next method.

Usage:
wait(time, units);

Parameters	Description
time	The amount of time to wait, as a positive integer.
units	The unit to represent the time: msec (default) – Milliseconds seconds.

int main() {
  // Initializing Robot Configuration. DO NOT REMOVE!
  vexcodeInit();
  // Stop driving after 1 second
  Drivetrain.drive(forward);
  wait(1, seconds);
  Drivetrain.stop();
}

for

for iterates over a code block for a set number of times.

Usage:

for (int i = 0; i <= count; i++) {

}

Parameters	Description
count	The amount of times that the code block will be iterated through.

int main() {
  // Initializing Robot Configuration. DO NOT REMOVE!
  vexcodeInit();
  // Drive in a square
  for (int i = 0; i < 4; i++) {
    Drivetrain.driveFor(forward, 100, mm);
    Drivetrain.turnFor(right, 90, degrees);
  }
}

if

if executes the indented block of code if the condition evaluates as true.

Usage:

if (condition) {
  
}

Parameters	Description
condition	An expression or variable that is evaluated when the statement runs. If it evaluates as true, the code inside the if block executes; if it evaluates as False, the block is skipped.

int main() {
  // Initializing Robot Configuration. DO NOT REMOVE!
  vexcodeInit();

  while (true) {
    if (Brain.Screen.pressing()) {
      // Display a message once the screen is pressed
      Brain.Screen.clearScreen();
      Brain.Screen.setCursor(1, 1);
      Brain.Screen.print("Screen pressed!");
      break;
    }
    wait(5, msec);
  }
}

if/else

if and else determine which indented block of code runs based on whether the condition evaluates as true or false.

Usage:

if (condition) {
  
}
else {
  
}

Parameters	Description
condition	An expression or variable that is evaluated when the statement runs. If it evaluates as true, the code inside the if block executes; if it evaluates as false, the code inside the else block executes instead.

int main() {
  // Initializing Robot Configuration. DO NOT REMOVE!
  vexcodeInit();

  while (true) {

    if (Brain.Screen.pressing()) {
      // Turn the screen green when pressed
      Brain.Screen.clearScreen(green);

    } else {
      Brain.Screen.clearScreen();
    }
  }
}

if/else if/else

The if/else if/else structure selects which indented block of code runs based on conditions:

• if runs its block if the condition evaluates as true.

• else if checks additional conditions only if all previous conditions evaluated as false. Multiple else if statements can be used.

• else runs its block only if none of the previous conditions evaluated as true.

Usage:

if (condition) {
  
}
else if (condition) {
  
}
else {
  
}

Parameters	Description
condition	An expression or variable that is evaluated when the statement runs. The first condition that evaluates as true determines which block executes; if none are true, the else block runs.

int main() {
  // Initializing Robot Configuration. DO NOT REMOVE!
  vexcodeInit();

  while (true) {
    
    // Turn screen blue if pressed on the left half
    if (Brain.Screen.pressing() && Brain.Screen.xPosition() < 240) {
      Brain.Screen.clearScreen(blue);

    // Turn screen green if pressed on the right half
    } else if (Brain.Screen.pressing() && Brain.Screen.xPosition() > 240) {
      Brain.Screen.clearScreen(green);

    } else {
      Brain.Screen.clearScreen();
    }

    wait(20, msec);
  }
}

while

while repeatedly runs methods as long as the condition is true. It can also be used like a “Wait until” by adding ! before the condition, as shown in the example below.

Usage:

while (condition) {
    
}

Parameters	Description
condition	An expression or variable that is evaluated before each iteration. If it evaluates as true, the loop continues; if it evaluates as false, the loop stops.

int main() {
  // Initializing Robot Configuration. DO NOT REMOVE!
  vexcodeInit();

  while (true) {
    if (Brain.Screen.pressing()) {
      // Turn the screen green whenever it's pressed
      Brain.Screen.clearScreen(green);
    } else {
      Brain.Screen.clearScreen();
    }
  }
}

int main() {
  // Initializing Robot Configuration. DO NOT REMOVE!
  vexcodeInit();

  // Wait until the screen is pressed to turn it green
  while (!Brain.Screen.pressing()) {
    wait(20, msec);
  }

  Brain.Screen.clearScreen(green);
}

break

break exits a loop immediately.

Usage:
break;

int main() {
  // Initializing Robot Configuration. DO NOT REMOVE!
  vexcodeInit();

  while (true) {

    // Press the screen to pause on a color
    Brain.Screen.clearScreen(red);
    wait(500, msec);

    if (Brain.Screen.pressing()) {
      break;
    }

    Brain.Screen.clearScreen(green);
    wait(500, msec);

    if (Brain.Screen.pressing()) {
      break;
    }
  }
}

programStop

programStop ends a running project.

Usage:
Brain.programStop();

Parameters	Description
	This method has no parameters.

int main() {
  // Initializing Robot Configuration. DO NOT REMOVE!
  vexcodeInit();

  while (true) {

    // Press the screen to stop the project
    Brain.Screen.clearScreen(red);
    wait(500, msec);

    if (Brain.Screen.pressing()) {
      Brain.programStop();
    }

    Brain.Screen.clearScreen(green);
    wait(500, msec);

    if (Brain.Screen.pressing()) {
      Brain.programStop();
    }
  }
}