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81 lines
3.3 KiB
Markdown
81 lines
3.3 KiB
Markdown
The [CONST](CONST) statement globally defines one or more named numeric or string values which will not change while the program is running.
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## Syntax
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> [CONST](CONST) constantName = value[, ...]
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## Parameter(s)
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* constantName is the constant name or list of names assigned by the programmer.
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* value is the value to initialize the global constant which cannot change once defined.
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* If constantName specifies a numeric type, value must be a numeric expression containing literals and other constants.
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* If constantName specifies a string type, the value must be a literal value.
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## Description
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* The constantName does not have to include a type suffix. The datatype is automatically infered by the compiler using the value.
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* Constant values cannot reference a variable or [FUNCTION](FUNCTION) return values.
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* The exception to the above are the internal functions: [_PI](_PI), [_ACOS](_ACOS), [_ASIN](_ASIN), [_ARCSEC](_ARCSEC), [_ARCCSC](_ARCCSC), [_ARCCOT](_ARCCOT), [_SECH](_SECH), [_CSCH](_CSCH), [_COTH](_COTH), [COS](COS), [SIN](SIN), [TAN](TAN), [LOG](LOG), [EXP](EXP), [ATN](ATN), [_D2R](_D2R), [_D2G](_D2G), [_R2D](_R2D), [_R2G](_R2G), [_G2D](_G2D), [_G2R](_G2R), [ABS](ABS), [SGN](SGN), [INT](INT), [_ROUND](_ROUND), [_CEIL](_CEIL), [FIX](FIX), [_SEC](_SEC), [_CSC](_CSC), [_COT](_COT), [ASC](ASC), [_RGB32](_RGB32), [_RGBA32](_RGBA32), [_RGB](_RGB), [_RGBA](_RGBA), [_RED32](_RED32), [_GREEN32](_GREEN32), [_BLUE32](_BLUE32), [_ALPHA32](_ALPHA32), [_RED](_RED), [_GREEN](_GREEN), [_BLUE](_BLUE), [_ALPHA](_ALPHA) (See Example 2 below).
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* Constants cannot be reassigned values. They retain the same value throughout all of the program procedures.
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* Constants defined in module-level code have [SHARED](SHARED) scope, so they can also be used in [SUB](SUB) or [FUNCTION](FUNCTION) procedures.
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* Constants defined in [SUB](SUB) or [FUNCTION](FUNCTION) procedures are local to those procedures.
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* [CLEAR](CLEAR) will not affect or change constant values.
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## Example(s)
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Display the circumference and area of circles:
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```vb
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' Declare a numeric constant approximately equal to the ratio of a circle's
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' circumference to its diameter:
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CONST PI = 3.141593
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' Declare some string constants:
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CONST circumferenceText = "The circumference of the circle is"
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CONST areaText = "The area of the circle is"
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DO
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INPUT "Enter the radius of a circle or zero to quit"; radius
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IF radius = 0 THEN END
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PRINT circumferenceText; 2 * PI * radius
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PRINT areaText; PI * radius * radius ' radius squared
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PRINT
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LOOP
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```
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```text
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Enter the radius of a circle or zero to quit? *10*
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The circumference of the circle is 62.83186
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The area of the circle is 314.1593
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Enter the radius of a circle or zero to quit? *123.456*
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The circumference of the circle is 775.697
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The area of the circle is 47882.23
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Enter the radius of a circle or zero to quit? *0*
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```
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> *Explanation:* PI cannot change as it is a mathematical constant so it is fitting to define it as a constant. Trying to change PI will result in a calculation error.
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*Example 2*: Using _RGB32 to set a constant's value.
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```vb
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CONST Red = _RGB32(255,0,0)
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COLOR Red
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PRINT "Hello World"
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```
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## See Also
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* [DIM](DIM), [SHARED](SHARED)
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* [STATIC](STATIC), [COMMON](COMMON)
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* [_PI](_PI), [_RGB32](_RGB32), [_RGBA32](_RGBA32)
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* [Windows 32 API constant values](http://doc.pcsoft.fr/en-US/?6510001)
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