Product SiteDocumentation Site Using Variables

There are three words that describe the key stages of using a variable: declaration, initialization, and assignment.
A variable must be declared before use, so that the interpreter knows that you want to use that symbol as a variable. All variables must be declared before any statement that does not declare a variable; in other words, you should declare your variables before doing anything else. Variable names are declared like this:
var variableName;
Variables can also be declared in lists, like this:
var variableName, variableOtherName;
Variables can be assigned a value at any time after they have been declared. Any single object can be assigned to a variable. If a variable is already assigned a value, any subsequent assignment will erase the previous assignment; the previously-assigned value will is not retrievable.
The first assignment to a variable is said to "initialize" the variable. Initialization is a special kind of assignment, because a variable cannot be used before it is initialized. If a program attempts to use an un-initialized variable, the SuperCollider interpreter will cause an error. For this reason, you should always initialize a variable when you declare it. There is a special way to do this:
var variableName = nil;
Since you can't always assign a useful value, you can pick an arbitrary one. Assigning "nil" is common practice, because it means "nothing," but without actually being nothing (this avoids some errors). Assigning zero is another possibility; it is standard practice in many programming languages, and will avoid most errors, even if the variable is eventually supposed to hold another kind of object. Intialization and declaration of multiple variables can also be done as a list:
var variableName = 0, variableOtherName = 0;
Single-letter variable names have a special purpose in SuperCollider. They are already declared, so you don't have to declare them. They are also already initialized to "nil", so you don't have to do that either. These variable names are intended to be used as a quick fix, while you're experimenting with how to make a program work. You should not use them in good-quality programs.
The single-letter variable "s" is automatically assigned to the server on the computer running the interpreter. You should avoid re-assigning that variable.
Variable names must always begin with a lower-case letter.
Use variables to write programs that do the following tasks:
  1. Perform arithmetic with an uninitialized variable. An error should appear when the program is executed.
  2. Calculate the value of y, if all other values are known, for the quadratic equation: y = a * x * x + b * x + c
  3. Re-write the Hello World Program so that it will say "Hello" to a name stored in a variable. Remember that you can use the interpreter to automatically output the last line of a function.