FreeBasic Const Keyword

last modified June 16, 2025

The FreeBasic Const keyword is used to declare constants - values that cannot be modified during program execution. Constants make code more readable and maintainable by replacing magic numbers with meaningful names.

Basic Definition

In FreeBasic, Const declares an identifier whose value remains fixed throughout the program. Constants must be initialized when declared and cannot be changed later.

Constants improve code clarity by giving meaningful names to values. They also prevent accidental modification of important values. FreeBasic supports numeric, string, and Boolean constants.

Basic Constant Declaration

This example shows the simplest form of constant declaration.

basic_const.bas

Const PI = 3.1415926535
Const MAX_USERS = 100
Const APP_NAME = "My Application"

Print "PI: "; PI
Print "MAX_USERS: "; MAX_USERS
Print "APP_NAME: "; APP_NAME

Here we declare three constants with different data types. PI is a floating-point constant, MAX_USERS is an integer, and APP_NAME is a string. Constants follow the same naming rules as variables but cannot be reassigned.

Typed Constants

Constants can have explicit type declarations for better type safety.

typed_const.bas

Const VERSION As Single = 1.2
Const TIMEOUT As Integer = 30
Const ENABLED As Boolean = True

Print "VERSION: "; VERSION
Print "TIMEOUT: "; TIMEOUT
Print "ENABLED: "; ENABLED

This example demonstrates typed constants. The As clause specifies the data type explicitly. Typed constants help prevent type-related errors and make the code more self-documenting.

Constant Expressions

Constants can be initialized with expressions evaluated at compile time.

const_expr.bas

Const HOURS_PER_DAY = 24
Const MINUTES_PER_HOUR = 60
Const MINUTES_PER_DAY = HOURS_PER_DAY * MINUTES_PER_HOUR

Print "Minutes in a day: "; MINUTES_PER_DAY

Const CIRCLE_DEGREES = 360
Const RIGHT_ANGLE = CIRCLE_DEGREES / 4
Print "Right angle: "; RIGHT_ANGLE

Here we use constant expressions to calculate new constants. The compiler evaluates these expressions during compilation. This allows for maintainable calculations that don't incur runtime overhead.

String Constants

String constants are useful for fixed text values used throughout a program.

string_const.bas

Const WELCOME_MSG = "Welcome to FreeBasic!"
Const PROMPT = "Enter your name: "
Const ERROR_404 = "404 - Page not found"

Print WELCOME_MSG
Print PROMPT
Input name$
Print "Hello, "; name$; "!"
Print ERROR_404

This example shows string constants for user interface messages. Using constants for strings makes it easier to maintain and localize applications. Changes only need to be made in one place.

Array Constants

FreeBasic allows creating constant arrays for fixed data sets.

array_const.bas

Const DAYS(1 To 7) As String = ("Sunday", "Monday", "Tuesday", _
                               "Wednesday", "Thursday", "Friday", _
                               "Saturday")

For i As Integer = 1 To 7
    Print "Day "; i; ": "; DAYS(i)
Next

Here we declare a constant array of weekday names. The array size and contents are fixed at compile time. Constant arrays are useful for lookup tables and other immutable data collections.

Scope of Constants

Constants follow the same scoping rules as variables in FreeBasic.

const_scope.bas

Const GLOBAL_CONST = 42

Sub TestScope
    Const LOCAL_CONST = 100
    Print "Local constant: "; LOCAL_CONST
    Print "Global constant: "; GLOBAL_CONST
End Sub

TestScope
Print "Global constant: "; GLOBAL_CONST
' Print LOCAL_CONST ' This would cause an error

This example demonstrates constant scope. GLOBAL_CONST is accessible throughout the program, while LOCAL_CONST is only visible within the TestScope subroutine. Constants declared in procedures are local to that procedure.

Enumerated Constants

FreeBasic supports enumerated constants for related values.

enum_const.bas

Enum Colors
    RED = 1
    GREEN = 2
    BLUE = 4
End Enum

Const BACKGROUND As Colors = BLUE
Const FOREGROUND As Colors = GREEN

Print "Background color code: "; BACKGROUND
Print "Foreground color code: "; FOREGROUND

This example shows enumerated constants for color values. Enums create a set of related named constants. They improve code readability by replacing magic numbers with meaningful names.

Best Practices

Naming: Use ALL_CAPS with underscores for constant names.
Organization: Group related constants together.
Documentation: Comment constants that aren't self-explanatory.
Scope: Use the smallest possible scope for constants.
Types: Specify types for important constants.

This tutorial covered the FreeBasic Const keyword with practical examples showing its usage in different scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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