Structure of a Program

Like any other computer program, Unigine script program is a sequence of instructions that tell the computer what to do. Lets take a quick look at the basic components of the UnigineScript program.

The most common type of instructions in a program is the statement. A statement in UnigineScript is the smallest independent unit in the language. We write statements in order to convey to the interpreter that we want to perform a task. Statements in UnigineScript are terminated by a semicolon.

The most common types of simple statements:

int x;

int x is a declaration statement. It tells the interpreter that x is a variable. All variables in a program must be declared before they are used.

x = 5;

x = 5 is an assignment statement. It assigns a value (5) to a variable (x).

The interpreter is also capable of resolving expressions. An expression is a mathematical entity that evaluates to a value. Expressions can involve values (such as 2), variables (such as x), operators (such as +) and functions. They can be singular (such as 2, or x), or compound (such as 2 + 3, 2 + x, x + y, or (2 + x)*(y - 3)).

x = 2 + 3;

x = 2 + 3 is a valid assignment statement. The expression 2+3 evaluates to the value of 5. This value of 5 is then assigned to x.

A variable is the name for a place in the computer's memory where you store some data. To be distinguished from others each variable needs an identifier (a sequence of characters used to name the variable, type, class, function etc.) In UnigineScript variables are declared to be of a type (however, the language uses dynamic typing in fact).

Here is an example of a variable declaration.

int x; // x - identifier, int - type

For example:

int foo() {
	int i;
	return i++;
}

log.message("%d\n",foo());

// the output is: 0,1,2,3...

You can also specify a reference variable if you want to allow your function to modify passed values:

void foo(int &v) {
	if(v) log.message("%d\n",v);
	v = 13;
}

int v = 0;
foo(v);
foo(v);

// the output is: 13

UnigineScript supports both single- and multi-line comments. Comments are ignored during code execution.

1. Single-line comments. Everything starting from // to the end of a line is a comment:
   Source code (UnigineScript)

   // single-line comment
   int x; // one more comment

2. Everything between /* and */ is a multi-line comment:
   Source code (UnigineScript)

   /* multi-line comment:
    * comment line
    * one more line
    */
   
   int foo() {
   	return 0;
   }

In UnigineScript, statements are typically grouped into units called functions. A function is a collection of statements that executes sequentially. Read more information about functions.

Libraries are groups of functions that have been “packaged up” for reuse in many different programs. The core UnigineScript language is actually very small and minimalistic — however, UnigineScript comes with a bunch of libraries, that provide programmers with lots of extra functionality. To include the library in your program use Preprocessor Directives.