Game Lab Documentation

For loop

Category:Control

Instead of typing a block of statements again and again, you can use a for loop around the block of statements. The most common usage of a for loop is simply to use it as a counting loop to execute a block of code a certain number of times.

Here is a typical construct for loop used to count from 0 to 3 to execute the block of code 4 times:

for(var i = 0; i < 4; i++)

initialization var i = 0; is executed once, before anything else. Create an identifier named i and initialize it to 0.

condition i < 4; is checked before each iteration, to see if the block of statements should execute or not. If i is less than 4.

increment i++ is executed after every iteration, after the block of statements is executed. Increase (increment) i by 1.

Examples

Basic Example

// Draw 4 dots along a line.
for(var i=0; i<4; i++){
	dot(5);
	moveForward();
}

Example: Count Down

Count down to zero from ten using a negative increment.

// Count down to zero from 10.
for(var i=10; i>0; i--){
    write(i) ;
}
write('Blast Off!');

Example: One Inch

Draw 8 tic marks along a line.

penUp();
turnLeft();
moveForward(100);
turnLeft(180);
penDown();
for(var i=0; i<7; i++){
    ticMark();
    moveForward();
}
ticMark();
penUp();
moveForward();

function ticMark() {
    turnLeft();
    moveForward(5);
    turnLeft(180);
    moveForward(5); 
    turnLeft();  
}

Example: Rake

Draw a rake ranging the angles from -45 to 45 by 5s.

// Draw a rake ranging the angles from -45 to 45 by 5s.
for(var angle=-45; angle<=45; angle=angle+5){
	turnTo(angle);
	moveForward(100);
	turnLeft(180);
	moveForward(100);
}
turnTo(180);
moveForward(200);

Example: Flower

Draw a flower with a parameter number of petals. Works best for petalCount between 5 and 10.

// Draw a flower with a parameter number of petals. Works best for petalCount between 5 and 10.
drawFlower(5);
function drawFlower(petalCount) {
penColor("pink");
penUp();
for(var i=0; i<360; i=i+(360/petalCount)){
turnTo(i);
moveForward(360/petalCount);
dot((2/3)*360/petalCount);
moveForward(-360/petalCount);
}
penColor("blue");
dot(360/petalCount/2);
}

Example: Random Die Rolls

Simulate rolling a die using a random number from 1 to 6, and roll the die 10000 times to check if the expected roll is 3.5.

// Simulate rolling a die using a random number from 1 to 6, and roll the die 10000 times to check if the expected roll is 3.5.
var sum = 0;
for (var i = 0; i < 10000; i++) {
    sum = sum + randomNumber(1,6);
}
console.log(sum/10000);

Syntax

for (initialization; condition; increment) { // block of statements }

Parameters

Name	Type	Description
initialization	AppLab Expression	Executed once, before anything else.
condition	Boolean expression	Checked before each iteration, to see if the block of statements should execute or not.
increment	AppLab Expression	Executed after every iteration, after the block of statements is executed.

Tips

You do not need to use i in the for loop statement, you can use any declared and initialized identifier.
You can start (initialization) and end (condition) the loop at any values.
You can use any increment, positive or negative.
Be careful not to code an infinite loop where the condition is never false.
Be careful not to code a loop that never executes because the condition is never true.

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