% (modulo)

Calculates the remainder when one number is divided by another. For example, when 52.1 is divided by 10, the divisor (10) goes into the dividend (52.1) five times (5 * 10 == 50), and there is a remainder of 2.1 (52.1 - 50 == 2.1). Thus, 52.1 % 10 produces 2.1.

Note that when the divisor is greater than the dividend, the remainder constitutes the value of the entire dividend. That is, a number cannot be divided by any number larger than itself. For example, when 9 is divided by 10, the result is zero with a remainder of 9. Thus, 9 % 10 produces 9.

Modulo is extremely useful for ensuring values stay within a boundary, such as when keeping a shape on the screen. (See the second example above.)

• int a = 5 % 4; // Sets 'a' to 1
  int b = 125 % 100; // Sets 'b' to 25
  float c = 285.5 % 140.0; // Sets 'c' to 5.5 
  float d = 30.0 % 33.0; // Sets 'd' to 30.0
  

• int a = 0;
  void draw() {
   background(200);
   a = (a + 1) % width; // 'a' increases between 0 and width 
   line(a, 0, a, height);
  }
  

• value1 % value2

• value1int or float
• value2int or float

• int or float

• divide