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https://github.com/QB64Official/qb64.git
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74 lines
2.8 KiB
Text
74 lines
2.8 KiB
Text
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{{KW|_UNSIGNED}} defines a numerical value as being positive using '''QB64''' only.
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''TYPE'' {{PageSyntax}}
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::: [[DIM]] variable [[AS]] [{{KW|UNSIGNED}}] ''datatype''
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::: variable [[AS]] [{{KW|_UNSIGNED}}] ''datatype''
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''_DEFINE'' {{PageSyntax}}
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::: {{KW|_DEFINE}} {{Parameter|LetterRange}} {{KW|AS}} [{{KW|_UNSIGNED}}] {{Parameter|datatype}}
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{{PageDescription}}
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* When {{KW|_UNSIGNED}} values use negative values the result subtracts from the highest value of the number's type keeping it positive.
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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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* {{KW|_UNSIGNED}} can be used in a {{KW|_DEFINE}} statement to set undefined variable name first letters as all positive only values.
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* Can also be used in {{KW|DIM}} statements or Subprocedure parameter definitions following {{KW|AS}}.
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* {{KW|_UNSIGNED}} allows larger positive numerical variable value limits than signed ones.
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* The Unsigned variable type suffix used is the '''tilde ~''' before the number's own type suffix: variablename~&
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<center>How negative values affect the {{KW|_UNSIGNED}} value returned by a {{KW|_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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''Example:'' 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 {{KW|_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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* [[ABS]], [[SGN]]
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* [[Variable Types]]
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{{PageNavigation}}
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