FreeBasic Double Keyword

last modified June 16, 2025

The FreeBasic Double keyword represents a double-precision floating-point data type. It provides greater range and precision than the Single type, making it suitable for scientific and financial calculations.

Basic Definition

In FreeBasic, Double is a 64-bit floating-point data type. It can store values from approximately ±5.0×10⁻³²⁴ to ±1.7×10³⁰⁸ with 15-16 significant digits of precision.

Double variables are essential for calculations requiring high precision or dealing with very large/small numbers. They follow the IEEE 754 standard for floating-point arithmetic.

Declaring Double Variables

This example shows how to declare and initialize Double variables.

double_declare.bas

Dim pi As Double = 3.141592653589793
Dim distance As Double = 1.495978707e8 ' km to Sun
Dim tinyValue As Double = 1.0e-300

Print "Pi: "; pi
Print "Distance to Sun: "; distance; " km"
Print "Tiny value: "; tinyValue

Here we declare three Double variables with different magnitudes. The first stores π with high precision. The second shows scientific notation for large numbers. The third demonstrates extremely small values.

Double Arithmetic Operations

Double variables support all standard arithmetic operations with high precision.

double_arithmetic.bas

Dim x As Double = 123456789.123456789
Dim y As Double = 987654321.987654321

Print "Addition: "; x + y
Print "Subtraction: "; y - x
Print "Multiplication: "; x * y
Print "Division: "; y / x
Print "Square root: "; Sqr(x)

This example demonstrates basic arithmetic with Double values. Note how the operations maintain precision even with large numbers. The Sqr function returns a Double result.

Double Precision Comparison

Comparing floating-point values requires special consideration due to precision limitations.

double_comparison.bas

Dim a As Double = 0.1 + 0.2
Dim b As Double = 0.3

Print "a = "; a
Print "b = "; b
Print "a == b: "; (a = b)
Print "Approximately equal: "; (Abs(a - b) < 0.0000001)

Due to binary floating-point representation, 0.1 + 0.2 doesn't exactly equal 0.3. This shows why exact equality comparisons often fail with floating-point numbers. We use an epsilon comparison instead.

Double in Mathematical Functions

Many mathematical functions return or accept Double values for precision.

double_math.bas

Dim angle As Double = 45.0 ' degrees
Dim radians As Double = angle * (3.141592653589793 / 180.0)

Print "Sin: "; Sin(radians)
Print "Cos: "; Cos(radians)
Print "Tan: "; Tan(radians)
Print "Log: "; Log(100.0)
Print "Exp: "; Exp(1.0)

This demonstrates trigonometric and logarithmic functions using Double values. The functions return Double results, maintaining precision through calculations. Note the degree to radian conversion.

Double Arrays

Arrays of Double values are useful for scientific and engineering data.

double_array.bas

Dim temperatures(1 To 5) As Double = { 98.6, 101.2, 97.9, 99.4, 100.1 }

Dim sum As Double = 0.0
For i As Integer = 1 To 5
    sum += temperatures(i)
Next

Dim average As Double = sum / 5.0
Print "Average temperature: "; average

This example stores temperature readings in a Double array. We calculate the average while maintaining precision. Double arrays are ideal for numerical data processing.

Double Type Conversion

FreeBasic can convert between Double and other numeric types.

double_conversion.bas

Dim d As Double = 123.456
Dim i As Integer = d
Dim s As Single = d

Print "Double: "; d
Print "To Integer: "; i
Print "To Single: "; s
Print "Back to Double: "; CDbl(i)

This shows implicit and explicit conversions. Converting to Integer truncates the decimal. Converting to Single may lose precision. The CDbl function converts back to Double.

Double Special Values

Double can represent special floating-point values like infinity and NaN.

double_special.bas

Dim inf As Double = 1.0 / 0.0
Dim nan As Double = 0.0 / 0.0

Print "Infinity: "; inf
Print "NaN: "; nan
Print "Is Infinity: "; IsInfinity(inf)
Print "Is NaN: "; IsNaN(nan)

This demonstrates special Double values. Division by zero creates infinity. 0/0 creates NaN (Not a Number). FreeBasic provides functions to detect these special cases.

Best Practices

Precision: Use Double when Single precision is insufficient.
Comparisons: Avoid exact equality checks with floating-point.
Performance: Be aware Double operations may be slower than Single.
Memory: Consider memory usage with large Double arrays.
Formatting: Use appropriate formatting when displaying Double values.

This tutorial covered the FreeBasic Double 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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