Goals

• To understand loops
  • while loop
  • for loop
  • Nested loop
  • for-each loop

Loops

We use loops to repeatedly execute a block of code. There are two main types of loops:
counter controlled loops and sentinel controlled loops.

A counter controlled loop uses a counter to control the number of times it executes. We call each time a loop runs an iteration.

A sentinel-controlled loop uses a boolean expression or flag to indicate how many times to iterate. It will iterate until the boolean expression is false.

Note: You can use break; in any of these loops to exit out of a statement early.

while loop

The basic pattern:

while( expressionThatIsTRUE){ //do something }

Here is an example of a sentinel-controlled while loop.

while(mouseX < width/2){ // do something }

Here is an example of a counter-controlled while loop.

int count = 0; while(count < 5){ //do something count++; }

Note: you can decided whether the counter should be updated before or after the code is executed. Beware of the difference.

for loop

A for loop is a counter-controlled loop. The counter declaration and increment are part of the loops syntax. The loop increments after each iteration.

// the basic pattern for(initialize variable ; condition ; "increment"){ // do something } // An example for(int i= 0; i < 10; i++){ // do something }

You can do more than just increment the variable. You can decrement/ multiple/ divide, or whatever arithmetic your design requires.

// this loop counts down by twos from 100 for(int i= 100; i => 0; i -= 2){ // do something }

for-each loop

There is a special type of for loop for working with collections. Collections are a generic way for referring to arrays, lists, and other data structures. They are handy because they require less typing.

The loop reads: for each item, with a given type, in the collection do what is included in the brackets. The type of the loop variable must match the type of the data stored in the collection.

The basic pattern:

// for-each item in the collection. for( type loopVariable : collection){ // statements }

A specific example:

void setup(){ size(400, 400); background(255); // declare an array of integers int numApples = 3; int [] apples = new int[numApples]; apples[0] = 100; apples[1] = 200; apples[2] = 300; for(int i: apples){ // draw apple pushMatrix(); translate(i, height/2); fill(255, 10, 0); ellipse(0,0, 30, 30); //draw leaf pushMatrix(); translate(0, -19); rotate(-PI/3); fill(5, 240, 0); ellipse(0,0, 15, 5); popMatrix(); popMatrix(); } }

Nested loops

A nested loop is simply a loop inside of loop. We can add a loop anywhere where we can put "statements."

while(somethingistrue){ //do some stuff // print five ellipses for(int i = 0; i < 5; i++){ ellipse(i * 10, height/2, 50, 50); } }

More on this later. . .

// global diameter control int diameter = 100; void setup() { size(400, 400); smooth(); background(255); } void draw() { //clear background background(255); // acceleration with a gradient of color float redValue = 0; //circle offset float offset = diameter/2; while (offset < width && redValue < 255) { // draw the circle pushMatrix(); translate(offset, offset); //set the circle to the correct red color fill(redValue, 0, 0, 128); ellipse(0, 0, diameter, diameter); popMatrix(); // update the offset by a factor. This will cause an acceleration effect offset *= (1 + (float) mouseX / (float) width); redValue += 32; } }