For loop

Category:Control

for loop

Category: Control

Executes a block of statements a certain number of times depending on the the initialization expression, conditional expression, and increment expression.

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.

Examples


// 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
}

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.

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.

Found a bug in the documentation? Let us know at documentation@code.org

Syntax

for(var i=0; i<4; i++){ //code }

Found a bug in the documentation? Let us know at documentation@code.org