Difference between revisions of "VARPTR$"

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'''VARPTR$''' is a memory function that returns a [[STRING]] representation of a variables address for use in a [[DRAW]] or [[PLAY]] statement.
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'''VARPTR$''' is a memory function that returns a [[STRING]] representation of a variable's memory address value for use in a [[DRAW]] or [[PLAY]] statement.
  
  
* When using this function with DRAW strings, use an = sign: TA= VARPTR$(n)
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{{PageSyntax}}
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:: string_value$ = VARPTR$(''variable'')
  
  
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* Can use any [[STRING|string]] or numerical variable reference '''existing''' in memory.
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* If the parameter value is from an array it must be dimensioned already. Cannot use fixed length string arrays.
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* When using '''numerical''' ''variable'' values in [[DRAW]] strings, use an = sign after the function letter. "TA=" + VARPTR$(''variable%'')
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* Always use variable X as in "X" + VARPTR$(''string_variable$'') to [[DRAW]] or [[PLAY]] another [[STRING]] value.
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* DRAW relative Moves use a + or - before the equal sign. EX: DRAW "M+=" + VARPTR$(x%) + ",-=" + VARPTR$(y%)
  
''See also:'' [[VARPTR]], [[DRAW]], [[PLAY]]
 
  
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''Example 1:'' How VARPTR$ reads consecutive values from memory.
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{{CodeStart}} '' ''
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{{Cl|SCREEN (statement)|SCREEN}} 2
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{{Cl|CLS}}
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WIND$ = "r10 d7 l10 u7 br20"  'create draw string to be read by function
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ROW$ = "x"+{{Cl|VARPTR$}}(WIND$)+"x"+{{Cl|VARPTR$}}(WIND$)+"x"+{{Cl|VARPTR$}}(WIND$)+" x"+{{Cl|VARPTR$}}(WIND$)+"bl80 bd11"
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{{Cl|LINE}} (100, 50)-(200, 160), , B
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{{Cl|DRAW}} "bm 115,52"
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{{Cl|FOR...NEXT|FOR}} I = 1 {{Cl|TO}} 10
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    {{Cl|DRAW}} "x" + {{Cl|VARPTR$}}(ROW$)
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{{Cl|NEXT}} '' ''
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{{CodeEnd}}
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:''NOTE:'' '''GWBasic''' allows '''semicolons''' to be used in the ROW$ definition, but QBasic and '''QB64''' MUST use '''+''' concatenation.
  
==Navigation:==
 
  
[[Keyword_Reference_-_Alphabetical|Go to Keyword Reference - Alphabetical]]
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''Example 2:'' Using the function to change a Turn Angle value using DRAW.
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{{CodeStart}} '' ''
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{{Cl|SCREEN (statement)|SCREEN}} 12
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                          'Demonstrates how string DRAW angles are used with TA
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{{Cl|FOR...NEXT|FOR}} i = 0 {{Cl|TO}} 360 {{Cl|STEP}} 30          'mark clock hours every 30 degrees
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  angle$ = {{Cl|STR$}}(i)                'change degree value i to a string 
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  {{Cl|PSET}} (175, 250), 6              'clock center
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  {{Cl|DRAW}} "TA" + angle$ + "BU100"    'add string angle to Turn Angle and draw blind up
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  {{Cl|CIRCLE}} {{Cl|STEP}}(0, 0), 5, 12        'place a circle at end of Up line
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  {{Cl|DRAW}} "P9, 12"
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  {{Cl|_DELAY}} .5         
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{{Cl|NEXT}}
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                            'Demonstrates how VARPTR$ is used with TA=
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{{Cl|DO}}: sec$ = {{Cl|RIGHT$}}({{Cl|TIME$}}, 2)        'get current second value from time
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  degree = {{Cl|VAL}}(sec$) * -6          'use a negative value to Turn Angle clockwise
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  {{Cl|PSET}} (175, 250), 9              'clock center
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  {{Cl|DRAW}} "TA=" + {{Cl|VARPTR$}}(degree) + "U90"  'VARPTR$ value requires = in DRAW
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  {{Cl|DO}}: {{Cl|_LIMIT}} 30: {{Cl|LOOP}} {{Cl|UNTIL}} {{Cl|RIGHT$}}({{Cl|TIME$}}, 2) <> sec$  'loop until seconds value changes
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  {{Cl|IF}} {{Cl|INKEY$}} <> "" {{Cl|THEN}} {{Cl|EXIT DO}}
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  {{Cl|PSET}} (175, 250), 0
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  {{Cl|DRAW}} "TA=" + {{Cl|VARPTR$}}(degree) + "U90"  'erase previous second hand draw
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{{Cl|LOOP}} '' ''
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{{CodeEnd}}
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:''Explanation:'' When the VARPTR$ value is used in DRAW, '''=''' MUST be used to pass the value to the draw! Negative Turn Angle values move clockwise and each second moves the hand 6 degrees. '''TA''' uses actual degree angles starting at 0 or noon.
  
[[Keyword Reference - By usage|Go to Keyword Reference - By usage]]
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''Example 3:'' Comparing DRAW moves using VARPTR$ and [[STR$]] values.
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{{CodeStart}} '' ''
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{{Cl|SCREEN}} 12
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{{Cl|PSET}} (200, 200), 12
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{{Cl|CIRCLE}} {{Cl|STEP}}(0, 0), 5, 10
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A = 100: B = 100
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{{Cl|DRAW}} "M+=" + {{Cl|VARPTR$}}(A) + ",-=" + {{Cl|VARPTR$}}(B)
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{{Cl|PSET}} (400, 400), 10
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{{Cl|CIRCLE}} {{Cl|STEP}}(0, 0), 5, 12
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C = 100: D = -100
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{{Cl|DRAW}} "M+" + {{Cl|STR$}}(C) + "," + {{Cl|STR$}}(D) 'must add + for positive relative moves
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{{Cl|END}} '' ''
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{{CodeEnd}}
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: ''Explanation:'' A negative STR$ value will move the DRAW relatively where VARPTR$ won't without the sign before the equal.
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''See also:''
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* [[VARPTR]], [[STR$]]
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* [[DRAW]], [[PLAY]]
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 +
 
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{{PageNavigation}}

Latest revision as of 13:10, 10 February 2021

VARPTR$ is a memory function that returns a STRING representation of a variable's memory address value for use in a DRAW or PLAY statement.


Syntax

string_value$ = VARPTR$(variable)


  • Can use any string or numerical variable reference existing in memory.
  • If the parameter value is from an array it must be dimensioned already. Cannot use fixed length string arrays.
  • When using numerical variable values in DRAW strings, use an = sign after the function letter. "TA=" + VARPTR$(variable%)
  • Always use variable X as in "X" + VARPTR$(string_variable$) to DRAW or PLAY another STRING value.
  • DRAW relative Moves use a + or - before the equal sign. EX: DRAW "M+=" + VARPTR$(x%) + ",-=" + VARPTR$(y%)


Example 1: How VARPTR$ reads consecutive values from memory.

SCREEN 2 CLS WIND$ = "r10 d7 l10 u7 br20" 'create draw string to be read by function ROW$ = "x"+VARPTR$(WIND$)+"x"+VARPTR$(WIND$)+"x"+VARPTR$(WIND$)+" x"+VARPTR$(WIND$)+"bl80 bd11" LINE (100, 50)-(200, 160), , B DRAW "bm 115,52" FOR I = 1 TO 10 DRAW "x" + VARPTR$(ROW$) NEXT

NOTE: GWBasic allows semicolons to be used in the ROW$ definition, but QBasic and QB64 MUST use + concatenation.


Example 2: Using the function to change a Turn Angle value using DRAW.

SCREEN 12 'Demonstrates how string DRAW angles are used with TA FOR i = 0 TO 360 STEP 30 'mark clock hours every 30 degrees angle$ = STR$(i) 'change degree value i to a string PSET (175, 250), 6 'clock center DRAW "TA" + angle$ + "BU100" 'add string angle to Turn Angle and draw blind up CIRCLE STEP(0, 0), 5, 12 'place a circle at end of Up line DRAW "P9, 12" _DELAY .5 NEXT 'Demonstrates how VARPTR$ is used with TA= DO: sec$ = RIGHT$(TIME$, 2) 'get current second value from time degree = VAL(sec$) * -6 'use a negative value to Turn Angle clockwise PSET (175, 250), 9 'clock center DRAW "TA=" + VARPTR$(degree) + "U90" 'VARPTR$ value requires = in DRAW DO: _LIMIT 30: LOOP UNTIL RIGHT$(TIME$, 2) <> sec$ 'loop until seconds value changes IF INKEY$ <> "" THEN EXIT DO PSET (175, 250), 0 DRAW "TA=" + VARPTR$(degree) + "U90" 'erase previous second hand draw LOOP

Explanation: When the VARPTR$ value is used in DRAW, = MUST be used to pass the value to the draw! Negative Turn Angle values move clockwise and each second moves the hand 6 degrees. TA uses actual degree angles starting at 0 or noon.


Example 3: Comparing DRAW moves using VARPTR$ and STR$ values.

SCREEN 12 PSET (200, 200), 12 CIRCLE STEP(0, 0), 5, 10 A = 100: B = 100 DRAW "M+=" + VARPTR$(A) + ",-=" + VARPTR$(B) PSET (400, 400), 10 CIRCLE STEP(0, 0), 5, 12 C = 100: D = -100 DRAW "M+" + STR$(C) + "," + STR$(D) 'must add + for positive relative moves END

Explanation: A negative STR$ value will move the DRAW relatively where VARPTR$ won't without the sign before the equal.


See also:



Navigation:
Keyword Reference - Alphabetical
Keyword Reference - By Usage
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