GCBASIC documentation
Variables

About Advanced Variable Types

A variable is an area of memory on the microcontroller that can be used to store a number or other data.   This is useful for many purposes, such as taking a sensor reading and acting on it, or counting the number of times the microcontroller has performed a particular task.

Each variable must be given a name, such as "MyVariable" or "PieCounter".   Choosing a name for a variable is easy - do not include spaces or any symbols (other than _), and make sure that the name is at least 2 characters (letters and/or numbers) long.

Advanced Types

There are a number different types of advanced variable types, and each type can store a different range of numeric information.  

With respect to advanced variables GCBASIC supports:

With respect to used advanced variables - please use Singles in your program as these have been tested. The other types are documented for completeness and should be used by developers in libraries.

Using advanced variable type maths is also much slower than integer maths when performing calculations and loops, therefore should be avoided if.   You should convert float calculations to integer maths to increase operation of your solution.   The example program (shown below) shows how use a float maths and you shuld try to do the same with integers and time the overall time for comparison.  Typically, floats are 18%-20% slower than similar integer maths operations.

The advanced variable types that GCBASIC supports are:

The format for single and double floats is defined by the IEEE 754 standard.   Sign, exponent and mantissa are all in the positions described here: https://www.geeksforgeeks.org/ieee-standard-754-floating-point-numbers/

Organisation of advanced variables

GCBASIC stores advanced variables in bytes.   The format of these bytes is:

_ D, _C, _B, _A, _E, _U, _H, variable_name  ( from high to Low)

You can access the bytes within advanced variables using the following as a guide using the suffixes _A, _B, _C etc.

Example of accessing the lowest byte, the _H, _U and the _A bytes.

    Dim workvariable as Single
    workvariable = 21845
    Dim lowb as byte
    Dim highb as byte
    Dim upperb as byte
    Dim lastb as byte


    lowb = workvariable
    highb = workvariable_H
    upperb = workvariable_U
    lastb = workvariable_A

Using the Byte components of Advanced Variables

This is strict. Accessing BYTE values of advanced variables requires the use cast. Failure to use cast will cause issue with the low byte ( the low byte will tranformed into a Long integer and you will provide the low byte of the Long integer).

Example. Mandated use of cast for single/float

    Dim sNumC as Single

    HserPrint "Hex with [CAST] / "
    HSerPrint "0x"
    HserPrint Hex([BYTE]sNumC_E)
    HserPrint Hex([BYTE]sNumC_U)
    HserPrint Hex([BYTE]sNumC_H)
    HserPrint Hex([BYTE]sNumC)
    HserPrintCRLF

Example assigning a HEX value to a single/float

  //  Assing 0x3F19999A equates to 0.6

    [BYTE]mySingle  = 0x9A      // Strict usage of BYTE cast to ensure the correct value is assinged the low byte of the single variable.
    mySingle_H= 0x99            // Assign _H byte
    mySingle_U= 0x19            // Assign _U byte
    mySingle_E= 0x3f            // Assign _E byte

Working example of assigning d0.5 or 0x3F000000 ( which is the IEEE574 hex value for d0.5 )

    // Decimal assignement
      mySingle = 0.5

    // Hex assignment
        [BYTE]mySingle  = [single]0x00
        mySingle_H      = 0x00
        mySingle_U      = 0x00
        mySingle_E      = 0x3f

Using Advanced Variables

Advanced variables must be "DIMensioned" first.  This involves using the DIM command, to tell GCBASIC that it is dealing with an advanced variable.

    Dim mySingle as Single
    mySingle= 1.1

    // The following types are for Libraries only

    Dim myLongInt as LongInt
    myLongInt = 9999999999999990          'see the Help for constraints

    Dim myuLongInt as uLongInt
    myuLongInt = 0xFFFFFFFFFFFFF          'see the Help for constraints

    Dim myDouble as Double
    myDouble=3.141592

Using Advanced Variables

Advanced variables are only supported by a subset of the functions of GCBASIC.  

The functional characteristics are:

Assigning Values to Advanced Variables

You can assign values to advanced variables using  `=`.  

A simple, but typical example follows.  This is the typical for numeric variable assignment.

    Dim mySingle as Single
    mySingle = 123.4567       'assign the value

Another example is bitwise assignments as follows:

    mySingle.16 = 1  'set the single bit to 1

+

INT() and SINGLRROUND()

Floating point numbers are not exact, and may yield unexpected results when compared using conditions (IF etc).   For example 6.0 / 3.0 may not equal 2.0.   Users should instead check that the absolute value of the difference between the numbers is less than some small number.

These techniques can replace the INT() and SINGLEROUND() functions.

Alternative to INT()

Assignment of a Single variable to an Interger variable is supported.  

So, use the conversion from floating point to integer as this results in integer truncation.

        dim mySingleVar as Single
        mySingleVar = 2.9  'A float type variable

        dim myLongVar as Long
        myLongVar = mySingleVar ' will set myLongVar to 2

Alterntive tp ROUNDSSINGLE()

As an alternative to using the ROUNDSSINGLE() function.  

Create your own round conversion, add 0.5 to return the nearest integer.  As follows:

        'Add 0.5 to a single or double and then assign to an integer variable

        dim mySingleVar as Single
        mySingleVar = 2.9

        dim myLongVar as Long
        myLongVar= mySingleVar + [single]0.5

Example Program

This program shows the values of calculation of 4.5 * multiplied by a number ( 4.5 x a range of 0 to 40,000).   The program shows setting up the advanced variables, assigned a value and completing the multiplication of the initial value using a for-next loop.  

    HSerPrintCRLF 2
    HSerPrint "Maths test "
    HSerPrintCRLF 2

    DIM multiplier as Word
    DIM ccount as Single
    Dim result as Single

    HSerPrint "Use floats with multiplier maths"
    HSerPrintCRLF

    'Assign a value to the variable
    ccount   = 4.5

      'Do some maths... multiplier x ccount
      For  multiplier = 0 to 40000 step 2500

        HSerPrint SingleToString(ccount)
        HSerPrint " x "
        HSerPrint left(WordToString(multiplier)+"        ", 10 )
        HSerPrint " = "

        'Calculate the result
        result = multiplier * ccount
        HSerPrint left(SingleToString(result)+"          ", 10 )
        HSerPrintCRLF
      next

      Do Forever
      Loop

To check variables and apply logic based on their value, see If, Do, For, Conditions

For more help, see: Declaring variables with DIM, Setting Variables