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https://github.com/QB64Official/qb64.git
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89 lines
No EOL
3.4 KiB
Text
89 lines
No EOL
3.4 KiB
Text
{{DISPLAYTITLE:_UNSIGNED}}
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[[_UNSIGNED]] defines a numerical value as being only positive.
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{{PageSyntax}}
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: [[DIM]] {{Parameter|variable}} [[AS]] [{{KW|_UNSIGNED}}] {{Parameter|datatype}}
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: [[_DEFINE]] {{Parameter|letterRange}} [[AS]] [{{KW|_UNSIGNED}}] {{Parameter|datatype}}
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{{PageDescription}}
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* Datatype can be any of the following: [[INTEGER]], [[LONG]], [[_BIT]], [[_BYTE]], [[_INTEGER64]], [[_OFFSET]]
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*'''[[SINGLE]], [[DOUBLE]] and [[_FLOAT]] variable types cannot be _UNSIGNED.'''
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* [[_UNSIGNED]] can be used in a [[_DEFINE]] statement to set undefined variable name first letters as all positive-only values.
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* Can also be used in [[DIM]] statements or subprocedure parameter definitions following [[AS]].
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* [[_UNSIGNED]] allows larger positive numerical variable value limits than signed ones.
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* The unsigned variable type suffix used is the '''tilde (~)''', right before the number's own type suffix: {{Parameter|variableName~&}}
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<center>How negative values affect the [[_UNSIGNED]] value returned by a [[_BYTE]] (8 bits). </center>
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{{WhiteStart}}
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00000001 - unsigned & signed are both 1
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01111111 - unsigned & signed are both 127
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11111111 - unsigned is 255 but signed is -1
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11111110 - unsigned is 254 but signed is -2
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11111101 - unsigned is 253 but signed is -3
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{{WhiteEnd}}
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{{PageExamples}}
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''Example 1:'' In '''QB64''', when a signed [[INTEGER]] value exceeds 32767, the value may become a negative value:
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{{CodeStart}} '' ''
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i% = 38000
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{{Cl|PRINT}} i% '' ''
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{{CodeEnd}}{{OutputStart}}-27536
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{{OutputEnd}}
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:''Explanation:'' Use an [[_UNSIGNED]] [[INTEGER]] or a ~% variable type suffix for only positive integer values up to 65535.
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''Example 2:'' In '''QB64''', [[_UNSIGNED]] [[INTEGER]] values greater than 65535 cycle over again from zero:
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{{CodeStart}} '' ''
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i~% = 70000
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{{Cl|PRINT}} i~% '' ''
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{{CodeEnd}}{{OutputStart}} 4464
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{{OutputEnd}}
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:''Explanation:'' In QB64 an unsigned integer value of 65536 would be 0 with values increasing by the value minus 65536.
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''Example 3:'' Demonstrating how _UNSIGNED variables expand the [[INTEGER]] range.
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{{CodeStart}} '' ''
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{{Cl|DIM}} n {{Cl|AS}} {{Cl|_UNSIGNED}} {{Cl|INTEGER}}
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{{Cl|DIM}} pn {{Cl|AS}} {{Cl|_UNSIGNED}} {{Cl|INTEGER}}
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{{Cl|LOCATE}} 3, 6: {{Cl|PRINT}} "Press Esc to exit loop"
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{{Cl|FOR...NEXT|FOR}} n = 1 {{Cl|TO}} 80000
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{{Cl|_LIMIT}} 10000 ' 6.5 second loop
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{{Cl|LOCATE}} 12, 37: {{Cl|PRINT}} n ' display current value
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{{Cl|IF...THEN|IF}} n > 0 {{Cl|THEN}} pn = n ' find highest value
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{{Cl|IF...THEN|IF}} n = 0 {{Cl|THEN}} Count = Count + 1: {{Cl|LOCATE}} 14, 37: {{Cl|PRINT}} "Count:"; Count; "Max:"; pn
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{{Cl|IF...THEN|IF}} {{Cl|INP}}(&H60) = 1 {{Cl|THEN}} {{Cl|EXIT|EXIT FOR}} ' escape key exit
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{{Cl|NEXT}} n
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{{Cl|END}} '' ''
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{{CodeEnd}}
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{{OutputStart}}
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Press Esc to exit loop
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65462
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Count: 13 Max: 65535
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{{OutputEnd}}
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''Explanation:'' The maximum value can only be 65535 (32767 + 32768) so the FOR loop repeats itself. Remove the [[_UNSIGNED]] parts and run it again.
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{{PageSeeAlso}}
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* [[DECLARE]], [[SUB]], [[FUNCTION]]
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* [[DIM]], [[_DEFINE]]
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* [[DEFSTR]], [[DEFLNG]], [[DEFINT]], [[DEFSNG]], [[DEFDBL]]
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* [[INTEGER]], [[LONG]], [[_INTEGER64]]
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* [[ABS]], [[SGN]]
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* [[Variable Types]]
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{{PageNavigation}} |