// Learning Processing
  // Daniel Shiffman
  // http://www.learningprocessing.com
  
  // Example 5-1: Conditionals
  
  // Variables
  float r = 150;
  float g = 0;
  float b = 0;
  
  void setup() {
    size(200,200);
  }
  
  void draw() {
    // Draw stuff
    background(r,g,b);  
    stroke(255);
    line(width/2,0,width/2,height);
  
    // If the mouse is on the right side of the screen is equivalent to 
    // "if mouseX is greater than width divided by 2."
    if(mouseX > width/2) {
      r = r + 1; 
    } else {
      r = r - 1;
    }
  
    // If r is greater than 255, set it back to 255.  
    // If r is less than 0, set it back to 0.
    if (r > 255) {
      r = 255; 
    } else if (r < 0) {
      r = 0; 
    }
  }