REDIM: Difference between revisions

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A {{KW|REDIM}} statement can re-dimension one [[$DYNAMIC|dynamic]](flexible) [[Arrays|array]] or a [[comma]] separated list of arrays.
A [[REDIM]] statement can re-dimension one [[$DYNAMIC|dynamic]](flexible) [[Arrays|array]] or a [[comma]] separated list of arrays.




{{PageSyntax}}
{{PageSyntax}}
:[[REDIM]] [{{KW|_PRESERVE}}] [{{KW|SHARED}}] ArrayName[''typesuffix''] ({''max_element''|low_element[{{KW|TO}} ''upper_element'', ...]}) [{{KW|AS}} {{KW|TYPE|Type}}]
:[[REDIM]] [[[_PRESERVE]]] [[[SHARED]]] ArrayName[''typesuffix''] ({''max_element''|low_element[[[TO]] ''upper_element'', ...]}) [[[AS]] [[TYPE|Type]]]




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* {{Parameter|elements}} is the number of elements the array should hold. Use the optional [[TO]] {{Parameter|elements2}} to set a range.
* {{Parameter|elements}} is the number of elements the array should hold. Use the optional [[TO]] {{Parameter|elements2}} to set a range.
* '''Always use the same array [[TYPE]] suffix ([[AS]] type) or a new array type with the same name may be created.'''
* '''Always use the same array [[TYPE]] suffix ([[AS]] type) or a new array type with the same name may be created.'''
* REDIM cannot change [[$STATIC]] arrays created with a [[DIM]] statement unless the [[$DYNAMIC]] [[Metacommand]] is used!  
* REDIM cannot change [[$STATIC]] arrays created with a [[DIM]] statement unless the [[$DYNAMIC]] [[Metacommand]] is used!
* To create a dynamic array use the [[$DYNAMIC]] metacommand or use [[REDIM]] rather than [[DIM]] when first creating the array.
* To create a dynamic array use the [[$DYNAMIC]] metacommand or use [[REDIM]] rather than [[DIM]] when first creating the array.
* Use REDIM [[_PRESERVE]] to change the range or number of array elements without losing the remaining elements. Data may move up or down to accommodate those boundary changes.
* Use REDIM [[_PRESERVE]] to change the range or number of array elements without losing the remaining elements. Data may move up or down to accommodate those boundary changes.
* '''REDIM [[_PRESERVE]] cannot change the number of array dimensions or type!'''
* '''REDIM [[_PRESERVE]] cannot change the number of array dimensions or type!'''
* [[$DYNAMIC|Dynamic]] arrays MUST be [[REDIM]]ensioned if [[ERASE]] or [[CLEAR]] are used to clear the arrays as they no longer exist.  
* [[$DYNAMIC|Dynamic]] arrays MUST be [[REDIM]]ensioned if [[ERASE]] or [[CLEAR]] are used to clear the arrays as they no longer exist.
* When [[AS]] is used to declare the type, use [[AS]] to retain that type or it will change to [[SINGLE]]!
* When [[AS]] is used to declare the type, use [[AS]] to retain that type or it will change to [[SINGLE]]!
* '''NOTE: Many QBasic keyword variable names CAN be used with a [[STRING]] suffix($) ONLY! You CANNOT use them without the suffix, use a numerical suffix or use [[DIM]], [[REDIM]], [[_DEFINE]], [[BYVAL]] or [[TYPE]] variable [[AS]] statements!'''
* '''NOTE: Many QBasic keyword variable names CAN be used with a [[STRING]] suffix($) ONLY! You CANNOT use them without the suffix, use a numerical suffix or use [[DIM]], [[REDIM]], [[_DEFINE]], [[BYVAL]] or [[TYPE]] variable [[AS]] statements!'''
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''Example 1:'' The [[$DYNAMIC]] Metacommand allows an array to be re-sized using [[DIM]] and REDIM.
''Example 1:'' The [[$DYNAMIC]] Metacommand allows an array to be re-sized using [[DIM]] and REDIM.
{{CodeStart}} '' ''
{{CodeStart}}
'{{Cl|$DYNAMIC}}
'{{Cl|$DYNAMIC}}


{{Cl|INPUT}} "Enter array size: ", size  
{{Cl|INPUT}} "Enter array size: ", size
{{Cl|DIM}} Array(size)
{{Cl|DIM}} Array(size)


{{Cl|REDIM}} Array(2 * size)
{{Cl|REDIM}} Array(2 * size)


{{Cl|PRINT}} {{Cl|UBOUND}}(Array) '' ''
{{Cl|PRINT}} {{Cl|UBOUND}}(Array)
{{CodeEnd}}
{{CodeEnd}}




''Example 2:'' Shows the difference between REDIM and REDIM [[_PRESERVE]].
''Example 2:'' Shows the difference between REDIM and REDIM [[_PRESERVE]].
{{CodeStart}} '' ''
{{CodeStart}}
{{Cl|REDIM}} array(20)
{{Cl|REDIM}} array(20)
array(10) = 24
array(10) = 24
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{{Cl|REDIM}} array(15)
{{Cl|REDIM}} array(15)
{{Cl|PRINT}} array(10) '' ''
{{Cl|PRINT}} array(10)
{{CodeEnd}}
{{CodeEnd}}
{{OutputStart}}
{{OutputStart}}
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{{PageSeeAlso}}
{{PageSeeAlso}}
* [[Arrays]]  
* [[Arrays]]
* [[DIM]], [[SHARED]]
* [[DIM]], [[SHARED]]
* [[_PRESERVE]], [[ERASE]]
* [[_PRESERVE]], [[ERASE]]

Latest revision as of 00:53, 25 January 2023

A REDIM statement can re-dimension one dynamic(flexible) array or a comma separated list of arrays.


Syntax

REDIM [[[_PRESERVE]]] [[[SHARED]]] ArrayName[typesuffix] ({max_element|low_element[[[TO]] upper_element, ...]}) [[[AS]] Type]


Description

  • Can change the number of elements in an array (the present array data is lost unless _PRESERVE is used).
  • Dynamic array elements can also be sized or resized by a program user's entry.
  • The _PRESERVE option also allows the element range values to be moved upward or downward in QB64 only!
  • Array is the name of the array to be dimensioned or re-dimensioned.
  • elements is the number of elements the array should hold. Use the optional TO elements2 to set a range.
  • Always use the same array TYPE suffix (AS type) or a new array type with the same name may be created.
  • REDIM cannot change $STATIC arrays created with a DIM statement unless the $DYNAMIC Metacommand is used!
  • To create a dynamic array use the $DYNAMIC metacommand or use REDIM rather than DIM when first creating the array.
  • Use REDIM _PRESERVE to change the range or number of array elements without losing the remaining elements. Data may move up or down to accommodate those boundary changes.
  • REDIM _PRESERVE cannot change the number of array dimensions or type!
  • Dynamic arrays MUST be REDIMensioned if ERASE or CLEAR are used to clear the arrays as they no longer exist.
  • When AS is used to declare the type, use AS to retain that type or it will change to SINGLE!
  • NOTE: Many QBasic keyword variable names CAN be used with a STRING suffix($) ONLY! You CANNOT use them without the suffix, use a numerical suffix or use DIM, REDIM, _DEFINE, BYVAL or TYPE variable AS statements!
  • Warning! Do not use negative array upper bound index values as OS access or "Out of Memory" errors will occur!


Example 1: The $DYNAMIC Metacommand allows an array to be re-sized using DIM and REDIM. 

'$DYNAMIC

INPUT "Enter array size: ", size
DIM Array(size)

REDIM Array(2 * size)

PRINT UBOUND(Array)


Example 2: Shows the difference between REDIM and REDIM _PRESERVE. 

REDIM array(20)
array(10) = 24

PRINT array(10)

REDIM _PRESERVE array(30)
PRINT array(10)

REDIM array(15)
PRINT array(10)

 24
 24
 0
Explanation: REDIM without _PRESERVE erases the array data and cannot change the number of dimensions.


See also


Navigation:
Main Page with Articles and Tutorials
Keyword Reference - Alphabetical
Keyword Reference - By usage
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