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73 lines
3 KiB
Plaintext
73 lines
3 KiB
Plaintext
The [[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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{{PageSyntax}}
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: [[CONST]] {{Parameter|constantName}} = {{Parameter|value}}[, ...]
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{{Parameters}}
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* {{Parameter|constantName}} is the constant name or list of names assigned by the programmer.
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* {{Parameter|value}} is the value to initialize the global constant which cannot change once defined.
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** If {{Parameter|constantName}} specifies a numeric type, {{Parameter|value}} must be a numeric expression containing literals and other constants.
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** If {{Parameter|constantName}} specifies a string type, the {{Parameter|value}} must be a literal value.
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{{PageDescription}}
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* The {{Parameter|constantName}} does not have to include a type suffix. The datatype is automatically infered by the compiler using the {{Parameter|value}}.
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* Constant values cannot reference a variable, [[SUB]] or [[FUNCTION]] return values when defined.
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** The exception to the above are color functions [[_RGB32]] and [[_RGBA32]], which can be used in a CONST statement. 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]] or [[FUNCTION]] procedures.
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* Constants defined in [[SUB]] or [[FUNCTION]] procedures are local to those procedures.
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* [[CLEAR]] will not affect or change constant values.
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{{PageExamples}}
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''Example 1:'' Display the circumference and area of circles:
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{{CodeStart}}' 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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{{Cl|CONST}} PI = 3.141593
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' Declare some string constants:
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{{Cl|CONST}} circumferenceText = "The circumference of the circle is"
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{{Cl|CONST}} areaText = "The area of the circle is"
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{{Cl|DO...LOOP|DO}}
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{{Cl|INPUT}} "Enter the radius of a circle or zero to quit"; radius
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{{Cl|IF...THEN|IF}} radius = 0 {{Cl|IF...THEN|THEN}} {{Cl|END}}
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{{Cl|PRINT}} circumferenceText; 2 * PI * radius
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{{Cl|PRINT}} areaText; PI * radius * radius ' radius squared
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{{Cl|PRINT}}
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{{Cl|DO...LOOP|LOOP}}
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{{CodeEnd}}
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{{OutputStart}}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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{{OutputEnd}}
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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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{{CodeStart}} '' ''
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{{Cl|CONST}} Red = _RGB32(255,0,0)
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{{Cl|COLOR}} Red
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{{Cl|PRINT}} "Hello World"
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{{CodeEnd}}
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{{PageSeeAlso}}
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* [[DIM]], [[SHARED]]
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* [[STATIC]], [[COMMON]]
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* [[_PI]], [[_RGB32]], [[_RGBA32]]
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* [http://doc.pcsoft.fr/en-US/?6510001 Windows 32 API constant values]
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{{PageNavigation}}
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