Control #

Introduction #

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

Functions and Keywords #

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

wait – Pauses the project for a set amount of time.
for – Repeats a block of code a set number of times.
if – Runs a block of code if a condition is true.
if/else – Runs one block of code if a condition is true, or a different block if it is false.
if/else if/else – Checks multiple conditions in order and runs the first block whose condition is true.
while – Repeats a block of code while a condition remains true.
break – Exits the current loop immediately.
programStop – Ends the project immediately.

wait #

Pauses the project for a specific amount of time before moving to the next line of code.

Available Functions

void wait(
  double time,
  timeUnits units );

Parameters

Parameter	Type	Description
`time`	`double`	The amount of time to wait, as a positive `double`.
`units`	`timeUnits`	The unit to represent the time: `msec` (default) – Milliseconds or `seconds`

Return Values

This function does not return a value.

Examples

// Stop driving after 1 second
Drivetrain.drive(forward);
wait(1, seconds);
Drivetrain.stop();

for #

Repeats a block of code. The counting form runs a set number of times; the range-based form runs once for each item in a collection.

Syntax

1 — Counting loop — runs a fixed number of times.
for (int i = 0; i < count; i++) {
   // code block
}

2 — Range-based loop — runs once for each item in a collection.
for (type element : collection) {
   // code block
}

Parameters

Parameter	Type	Description
`count`	`int`	The number of times that the code block will be repeated.
`type`	Type Name	The data type of each item in the collection (e.g. `int`, `double`).
`element`	`variable`	The name of the variable to hold the value of the current item of the loop.
`collection`	`array`	The Array (or vector) that holds the items that will be looped through.

Return Values

This control structure does not return a value.

Examples

// Drive in a square
for (int i = 0; i < 4; i++) {
  Drivetrain.driveFor(forward, 100, mm);
  Drivetrain.turnFor(right, 90, degrees);
}

// Drive forward different distances
int distances[] = {100, 150, 200};
for (int d : distances) {
  Drivetrain.driveFor(forward, d, mm);
  wait(0.5, seconds);
}

if #

Runs the enclosed block of code if the condition is true.

Syntax

if (condition) {
  // code block
}

Parameters

Parameter	Type	Description
`condition`	`bool`	An expression or variable that is evaluated when the statement runs. If it is `true`, the code inside the `if` block runs; if it is `false`, the block is skipped.

Return Values

This control structure does not return a value.

Examples

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 #

Determines which enclosed block of code runs based on whether the condition is true or false.

Syntax

if (condition) {
  // code block if true
}
else {
  // code block if false
}

Parameters

Parameter	Type	Description
`condition`	`bool`	An expression or variable that is evaluated when the statement runs. If it is `true`, the code inside the `if` block runs; if it is `false`, the code inside the `else` block runs instead.

Return Values

This control structure does not return a value.

Examples

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

if/else if/else #

Selects which enclosed block of code runs based on multiple conditions.

Syntax

if (condition) {
  // code block if first condition is true
}
else if (condition) {
  // code block if second condition is true
}
else {
  // code block if no conditions are true
}

Parameters

Parameter	Type	Description
`condition`	`bool`	An expression or variable that is evaluated when the statement runs. The first condition that is `true` determines which block runs; if none are `true`, the `else` block runs.

Return Values

This control structure does not return a value.

Notes

if runs its block if the condition is true.
else if checks additional conditions only if all previous conditions are false. Multiple else if statements can be used.
else runs its block only if none of the previous conditions are true.

Examples

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 #

Repeatedly runs code as long as the condition is true.

Syntax

while (condition) {
  // code block
}

Parameters

Parameter	Type	Description
`condition`	`bool`	An expression or variable that is evaluated before each iteration. If it is `true`, the loop continues; if it is `false`, the loop stops.

Return Values

This control structure does not return a value.

Notes

It can also be used like a “Wait until” by adding ! before the condition, as shown in the examples below.

Examples

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

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

Brain.Screen.clearScreen(green);

break #

Exits the current loop immediately. If in a nested loop, break exits the innermost loop.

Syntax

break;

Parameters

This statement does not accept any parameters.

Return Values

This statement does not return a value.

Examples

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 #

Ends a project immediately.

Syntax

Brain.programStop();

Parameters

This statement does not accept any parameters.

Return Values

This statement does not return a value.

Examples

while (true) {

  // Press the screen to end 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();
  }
}