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The | 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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{{PageExamples}} | {{PageExamples}} | ||
;Example 1: Display the circumference and the area of circles: | |||
{{CodeStart}}' Declare a numeric constant approximately equal to the ratio of a circle's | {{CodeStart}} | ||
' circumference to its diameter: | {{Text|<nowiki>' Declare a numeric constant approximately equal to the ratio of a circle's</nowiki>|#919191}} | ||
{{Cl|CONST}} PI = 3.141593 | {{Text|<nowiki>' circumference to its diameter:</nowiki>|#919191}} | ||
{{Cl|CONST}} PI = {{Text|3.141593|#F580B1}} | |||
' Declare some string constants: | {{Text|<nowiki>' Declare some string constants:</nowiki>|#919191}} | ||
{{Cl|CONST}} circumferenceText = "The circumference of the circle is" | {{Cl|CONST}} circumferenceText = {{Text|<nowiki>"The circumference of the circle is"</nowiki>|#FFB100}} | ||
{{Cl|CONST}} areaText = "The area of the circle is" | {{Cl|CONST}} areaText = {{Text|<nowiki>"The area of the circle is"</nowiki>|#FFB100}} | ||
{{Cl | {{Cl|DO}} | ||
{{Cl|INPUT}} "Enter the radius of a circle or zero to quit"; radius | {{Cl|INPUT}} {{Text|<nowiki>"Enter the radius of a circle or zero to quit"</nowiki>|#FFB100}}; radius | ||
{{Cl | {{Cl|IF}} radius = {{Text|0|#F580B1}} {{Cl|THEN}} {{Cl|END}} | ||
{{Cl|PRINT}} circumferenceText; 2 * PI * radius | {{Cl|PRINT}} circumferenceText; {{Text|2|#F580B1}} * PI * radius | ||
{{Cl|PRINT}} areaText; PI * radius * radius ' radius squared | {{Cl|PRINT}} areaText; PI * radius * radius {{Text|<nowiki>' radius squared</nowiki>|#919191}} | ||
{{Cl|PRINT}} | {{Cl|PRINT}} | ||
{{Cl| | {{Cl|LOOP}} | ||
{{Cl|END}} | |||
{{CodeEnd}} | {{CodeEnd}} | ||
{{OutputStart}}Enter the radius of a circle or zero to quit? ''10'' | {{OutputStart}} | ||
Enter the radius of a circle or zero to quit? ''10'' | |||
The circumference of the circle is 62.83186 | The circumference of the circle is 62.83186 | ||
The area of the circle is 314.1593 | The area of the circle is 314.1593 | ||
| Line 47: | Line 50: | ||
Enter the radius of a circle or zero to quit? ''123.456'' | Enter the radius of a circle or zero to quit? ''123.456'' | ||
The circumference of the circle is 775.697 | The circumference of the circle is 775.697 | ||
The area of the circle is 47882. | The area of the circle is 47882.226 | ||
Enter the radius of a circle or zero to quit? ''0'' | Enter the radius of a circle or zero to quit? ''0'' | ||
{{OutputEnd}} | {{OutputEnd}} | ||
{{PreStart}} | |||
'''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. | |||
{{PreStart}} | |||
---- | |||
;Example 2: Using _RGB32 to set a constant's value. | |||
{{CodeStart}} | {{CodeStart}} | ||
{{Cl|CONST}} Red = _RGB32(255,0,0) | {{Cl|SCREEN}} {{Cl|_NEWIMAGE}}({{Text|640|#F580B1}}, {{Text|400|#F580B1}}, {{Text|32|#F580B1}}) | ||
{{Cl|CONST}} Red = {{Cl|_RGB32}}({{Text|255|#F580B1}}, {{Text|0|#F580B1}}, {{Text|0|#F580B1}}) | |||
{{Cl|COLOR}} Red | {{Cl|COLOR}} Red | ||
{{Cl|PRINT}} "Hello World" | {{Cl|PRINT}} {{Text|<nowiki>"Hello World"</nowiki>|#FFB100}} | ||
{{Cl|END}} | |||
{{CodeEnd}} | {{CodeEnd}} | ||
{{OutputStart}} | |||
{{Ot|Hello World|red}} | |||
{{OutputEnd}} | |||
Revision as of 14:45, 8 December 2024
The CONST statement globally defines one or more named numeric or string values which will not change while the program is running.
Syntax
- CONST constantName = value[, ...]
Parameters
- constantName is the constant name or list of names assigned by the programmer.
- value is the value to initialize the global constant which cannot change once defined.
- If constantName specifies a numeric type, value must be a numeric expression containing literals and other constants.
- If constantName specifies a string type, the value must be a literal value.
Description
- The constantName does not have to include a type suffix. The datatype is automatically infered by the compiler using the value.
- Constant values cannot reference a variable or user FUNCTION return value when defined. However, other (already known) constants and most of the internal char, math or color functions can be used, such as CHR$, EXP or _RGBA32.
- Constants cannot be reassigned values. They retain the same value throughout all of the program procedures.
- Constants defined in module-level code have shared scope, so they can also be used in SUB or FUNCTION procedures.
- Constants defined in SUB or FUNCTION procedures are local to those procedures.
- CLEAR will not affect or change constant values.
- Since QB64-PE v4.0.0 a huge list of preset Constants is available in every program.
Examples
- Example 1
- Display the circumference and the area of circles:
' Declare a numeric constant approximately equal to the ratio of a circle's ' circumference to its diameter: CONST PI = 3.141593 ' Declare some string constants: CONST circumferenceText = "The circumference of the circle is" CONST areaText = "The area of the circle is" DO INPUT "Enter the radius of a circle or zero to quit"; radius IF radius = 0 THEN END PRINT circumferenceText; 2 * PI * radius PRINT areaText; PI * radius * radius ' radius squared PRINT LOOP END |
Enter the radius of a circle or zero to quit? 10 The circumference of the circle is 62.83186 The area of the circle is 314.1593 Enter the radius of a circle or zero to quit? 123.456 The circumference of the circle is 775.697 The area of the circle is 47882.226 Enter the radius of a circle or zero to quit? 0 |
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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