Example

example_5_3

// Learning Processing
// Daniel Shiffman
// http://www.learningprocessing.com

// Example 5-3: Rollovers
void setup() {
  size(200,200);
}

void draw() {
  background(255);
  stroke(0);
  line(100,0,100,200);
  line(0,100,200,100);
  
  // Fill a black color
  noStroke();
  fill(0);

  // Depending on the mouse location, a different rectangle is displayed.    
  if (mouseX < 100 && mouseY < 100) {
    rect(0,0,100,100);
  } else if (mouseX > 100 && mouseY < 100) {
    rect(100,0,100,100);
  } else if (mouseX < 100 && mouseY > 100) {
    rect(0,100,100,100);
  } else if (mouseX > 100 && mouseY > 100) {
    rect(100,100,100,100);
  }
}

3 Comments
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  1. After a 20 year break from programming this excercise really grabbed my interest. After doing it as above I tried nested if statements (If mouse on left side of screen then if mouse at top of screen etc.) This didn’t make it any prettier.

    Then I remembered you could do this

    x=(width/2)*int(mouseX>width/2);
    y=(height/2)*int(mouseY > height/2);
    rect(x,y,width/2,height/2);

    What fun!

    Comment by Kit — July 27, 2009 @ 6:07 am

  2. I did this exercise only with ifs first i thought i made a mistake but it worked as well i am wondering what is the plus to use if else ?

    Thanks

    PM

    void setup() {
    size(200,200);
    }

    void draw() {
    background(255);
    stroke(0);
    line(100,0,100,200);
    line(0,100,200,100);

    // Fill a black color
    noStroke();
    fill(0);

    // Depending on the mouse location, a different rectangle is displayed.
    if (mouseX < 100 && mouseY 100 && mouseY < 100) {
    rect(100,0,100,100); }
    if (mouseX 100) {
    rect(0,100,100,100);}
    if (mouseX > 100 && mouseY > 100) {
    rect(100,100,100,100);
    }
    }

    Comment by Patrick Mimran — March 14, 2010 @ 10:16 am

  3. In this case, it doesn’t really matter, but an if/else structure will only allow the first instance of true to be executed whereas multiple if statements are treated separately. The following illustrates the point more effectively:

    
int x = 50;

if (x > 30) {
  println("A");
} else if (x > 20) {
  println("B");
}

if (x > 30) {
  println("C");
}

if (x > 20) {
  println("D");
}

    Comment by Daniel Shiffman — March 15, 2010 @ 10:05 am

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