Designing Games with Game Maker - YoYo Games

store either a real number or a string. Variables do not need to be declared like in many other
languages. There are a large number of built-in variables. Some are general, like mouse_x
and mouse_y that indicate the current mouse position, while all others are local to the object
instance for which we execute the program, like x and y that indicate the current position of
the instance. A variable has a name that must start with a letter and can contain only letters,
numbers, and the underscore symbol '_'. (The maximal length is 64 symbols.) When you use a
new variable it is local to the current instance and is not known in programs for other
instances (even of the same object). You can though refer to variables in other instances; see
below.
Assignments
An assignment stores a value in a variable. An assignment has the form:
= ;
An expression can be a simple value but can also be more complicated. Rather than assigning
a value to a variable, one can also add the value to the current value of the variable using +=.
Similar, you can subtract it using -=, multiply it using *=, divide it using /= ,or use bitwise
operators using |=, &\, or ^=.
Expressions
Expressions can be real numbers (e.g. 3.4), hexadecimal numbers, starting with a $ sign (e.g.
$00FFAA), strings between single or double quotes (e.g. 'hello' or “hello”) or more complicated
expressions. For expressions, the following binary operators exist (in order of priority):
• && || ^^: combine Boolean values (&& = and, || = or, ^^ = xor)
• < >=: comparisons, result in true (1) or false (0)
• | & ^: bitwise operators (| = bitwise or, & = bitwise and, ^ = bitwise xor)
• >: bitwise operators ( > = shift right)
• + -: addition, subtraction
• * / div mod: multiplication, division, integer division, and modulo
Note that value of x div y is the value of x/y rounded in the direction of zero to the nearest
integer. The mod operator returns the remainder obtained by dividing its operands. In other
words, x mod y = x - (x div y) * y. Also, the following unary operators exist: