Language

Language

The syntax and keywords of the language, which is the same in BlitzBasic, Blitz3D and BlitzPlus. Commands such as Print, Rect or CreateCube are in the Command-Index, this page is about what the compiler understands by itself. Every keyword and function below has its own page in Language Features. Keywords and names are not case sensitive, and ; starts a comment that lasts to the end of the line.

Variables and types

A variable has one of three types, which a suffix on its name says: % is an integer (also the default), # a float, $ a string. Variables you assign to are created on first use. Local makes a variable that only exists in its function, Global makes one that every function can see, and Const makes a name for a value that cannot change.

Const LIMIT = 3
Global total% = 0
For i = 1 To LIMIT
	total = total + i
Next
half# = total / 2.0
name$ = "sum"
Print name$ + " " + total + " " + half#

sum 6 3.0

Int, Float and Str convert between the types (Int rounds to the nearest whole number), and Handle and Object convert between an object and a number that stands for it.

Print Int(3.7)
Print Float(2) / 4
Print Str(12) + "!"

4
0.5
12!

Operators

Operators	Meaning
+ - * / ^	Arithmetic. Dividing two integers gives an integer, so use a float to get a fraction.
Mod	Remainder of a division.
Shl Shr Sar	Shift bits left, right, and right keeping the sign.
And Or Xor Not	Bitwise and logical operators.
= <> < > <= >=	Comparison. They give 1 for true and 0 for false.
Abs() Sgn() Pi	Absolute value, sign (-1, 0 or 1) and the number 3.14159.

Print 7 Mod 4
Print 1 Shl 4
Print -8 Sar 1
Print 5 Xor 1
Print Abs(-3)
Print Sgn(-2)

3
16
-4
4
3
-1

Control flow

x = 2
If x = 1
	Print "one"
ElseIf x = 2
	Print "two"
Else
	Print "many"
EndIf

Select x
	Case 1 : Print "case one"
	Case 2, 3 : Print "case two or three"
	Default : Print "default"
End Select

For i = 10 To 1 Step -4
	Print i
Next

While x < 4
	x = x + 1
Wend

Repeat
	x = x - 1
Until x <= 2
Print x

two
case two or three
10
6
2
2

Exit leaves the closest loop, Repeat ... Forever loops until Exit, Goto jumps to a .label, and Gosub calls the code at a label that ends with Return.

Functions

Function Double(n)
	Return n * 2
End Function

Function Greet$(name$, loud = 0)
	If loud Then Return Upper$(name$) + "!"
	Return name$
End Function

Print Double(21)
Print Greet$("hi")
Print Greet$("hi", 1)

42
hi
HI!

A suffix after the function name says what type it returns, and a parameter with = value is optional.

The parts of an expression are evaluated in the order of the original Blitz3D, which is not left to right, see Language Quirks.

Arrays

Dim makes an array whose indices go from 0 up to the number you give, so Dim a(3) has four elements.

Dim a(3)
a(2) = 5
Print a(2)
Dim grid(2, 2)
grid(1, 2) = 9
Print grid(1, 2)

5
9

Types

A Type describes a record with fields. New creates one, Delete removes it, and \ reads a field. Every type keeps a list of its objects, which First, Last, Before, After and For ... Each walk through, and Insert moves an object inside that list.

Type Point
	Field x, y
End Type

For i = 1 To 3
	p.Point = New Point
	p\x = i
Next

For p.Point = Each Point
	Print p\x
Next

Delete First Point
l.Point = Last Point
Print l\x

1
2
3
3

Delete frees the object at once and sets the variable it was given to Null (Delete First Point and Delete After p have no variable to set). Deleting an object that is Null does nothing, only the literal Delete Null is a runtime error. Inside For ... Each, the object of the loop and any other object of the type can be deleted. Insert Object Before Other and Insert Object After Other can also be used as an expression that gives the object back, such as c = Insert New Point Before First Point. A variable that still points at a deleted object keeps it alive and stops the program with Object does not exist. when it is used, in every build.

Data

Data holds values in the program, Read takes the next one, and Restore goes back to a label.

Restore numbers
Read a
Read b
Print a + b
.numbers
Data 3, 4

7

Restore also works inside a function: it goes to a label of the main program, which is where Data is.

A value can also be a calculation of constants, such as 40 - 170, 2 * 3.5 or "Blitz" + "LLVM". It is worked out while compiling, so it can not use variables.

Const Offset = 100
Restore values
Read a
Read b
Read c$
Print a + b
Print c
.values
Data 40 - 170, Offset * 2, "Blitz" + "LLVM"

70
BlitzLLVM

Other keywords

Include "file.bb" puts another source file in this place, True and False are 1 and 0, Null is the empty object, and End stops the program.