FreeBasic Dim Keyword

last modified June 16, 2025

The FreeBasic Dim keyword is used to declare variables and arrays. It allocates memory for data storage and optionally initializes variables. Understanding Dim is fundamental to FreeBasic programming.

Basic Definition

In FreeBasic, Dim stands for "dimension" and is used to declare variables with specific data types. It can declare single variables or arrays of variables. The syntax allows for initialization during declaration.

Variables declared with Dim have local scope by default when used inside procedures. At module level, they have module-wide scope. Proper use of Dim ensures efficient memory management.

Simple Variable Declaration

This example shows basic variable declaration using the Dim keyword.

simple_declaration.bas

Dim age As Integer
Dim fname As String
Dim price As Double = 19.99

age = 25
fname = "John Doe"

Print "Name: "; fname
Print "Age: "; age
Print "Price: "; price

Here we declare three variables of different types. The age and fname variables are declared first then assigned values later. price is initialized during declaration. Each variable has a specific data type.

Multiple Variable Declaration

Dim can declare multiple variables of the same type in one statement.

multiple_declaration.bas

Dim x As Integer, y As Integer, z As Integer
Dim firstName As String, lastName As String = "Smith"

x = 10
y = 20
z = x + y
firstName = "John"

Print "Full name: "; firstName; " "; lastName
Print "Sum: "; z

This example declares three integer variables in one line and two string variables in another. Note that initialization can be done for some variables while leaving others uninitialized. This makes code more concise.

Array Declaration

Dim is used to declare arrays with specified dimensions.

array_declaration.bas

Dim numbers(1 To 5) As Integer
Dim names(0 To 2) As String = {"Alice", "Bob", "Charlie"}

For i As Integer = 1 To 5
    numbers(i) = i * 10
Next

For i As Integer = 0 To 2
    Print names(i)
Next

For i As Integer = 1 To 5
    Print numbers(i)
Next

Here we declare two arrays: an integer array with indices 1 to 5 and a string array with indices 0 to 2. The string array is initialized during declaration. Arrays are fundamental for storing collections of data.

Dynamic Arrays

FreeBasic allows dynamic arrays whose size can be changed at runtime.

dynamic_array.bas

Dim dynamicArray() As Integer
Dim size As Integer = 3

ReDim dynamicArray(1 To size)

For i As Integer = 1 To size
    dynamicArray(i) = i * 100
Next

Print "Original array:"
For i As Integer = 1 To size
    Print dynamicArray(i)
Next

size = 5
ReDim Preserve dynamicArray(1 To size)

Print "Resized array:"
For i As Integer = 1 To size
    Print dynamicArray(i)
Next

This demonstrates dynamic array usage. We first declare an empty array, then use ReDim to set its size. ReDim Preserve resizes while keeping existing values. Dynamic arrays offer flexibility in memory usage.

Multi-dimensional Arrays

Dim can declare arrays with multiple dimensions.

multi_dim_array.bas

Dim matrix(1 To 3, 1 To 3) As Integer
Dim row As Integer, col As Integer

' Initialize matrix
For row = 1 To 3
    For col = 1 To 3
        matrix(row, col) = row * col
    Next
Next

' Print matrix
For row = 1 To 3
    For col = 1 To 3
        Print matrix(row, col); " ";
    Next
    Print
Next

This creates a 3x3 matrix (two-dimensional array). We use nested loops to initialize and print the array. Multi-dimensional arrays are useful for representing grids, tables, or matrices in mathematical operations.

Type Declaration

Dim can declare variables of user-defined types.

type_declaration.bas

Type Person
    name As String
    age As Integer
    height As Double
End Type

Dim student As Person
Dim teacher As Person = {"Mr. Smith", 45, 1.82}

student.name = "Alice"
student.age = 20
student.height = 1.65

Print "Student: "; student.name; ", "; student.age; ", "; student.height
Print "Teacher: "; teacher.name; ", "; teacher.age; ", "; teacher.height

Here we define a Person type and declare two variables of this type. One is initialized during declaration, the other is assigned values field by field. User-defined types help organize related data into logical units.

Static Variables

Dim can declare static variables that retain their values between calls.

static_variable.bas

Sub Counter()
    Static Dim count As Integer
    count += 1
    Print "Count: "; count
End Sub

For i As Integer = 1 To 5
    Counter()
Next

This example shows a static variable inside a procedure. Unlike regular local variables, static variables maintain their values between procedure calls. The count variable increments with each call to Counter.

Best Practices

Explicit Types: Always specify variable types for clarity.
Descriptive Names: Use meaningful variable names.
Initialization: Initialize variables when possible.
Scope: Declare variables in the smallest needed scope.
Arrays: Prefer 0-based or 1-based indexing consistently.

This tutorial covered the FreeBasic Dim keyword with practical examples showing its usage in different scenarios. Mastering Dim is essential for effective FreeBasic programming.

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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