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106 lines
3 KiB
Markdown
106 lines
3 KiB
Markdown
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[_UNSIGNED](_UNSIGNED) defines a numerical value as being only positive.
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## Syntax
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> [DIM](DIM) variable [AS](AS) [_UNSIGNED] datatype
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> [_DEFINE](_DEFINE) letterRange [AS](AS) [_UNSIGNED] datatype
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## Description
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* Datatype can be any of the following: [INTEGER](INTEGER), [LONG](LONG), [_BIT](_BIT), [_BYTE](_BYTE), [_INTEGER64](_INTEGER64), [_OFFSET](_OFFSET)
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***[SINGLE](SINGLE), [DOUBLE](DOUBLE) and [_FLOAT](_FLOAT) variable types cannot be _UNSIGNED.**
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* [_UNSIGNED](_UNSIGNED) can be used in a [_DEFINE](_DEFINE) statement to set undefined variable name first letters as all positive-only values.
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* Can also be used in [DIM](DIM) statements or subprocedure parameter definitions following [AS](AS).
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* [_UNSIGNED](_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: variableName~&
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How negative values affect the [_UNSIGNED](_UNSIGNED) value returned by a [_BYTE](_BYTE) (8 bits).
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```text
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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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```
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## Example(s)
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In **QB64**, when a signed [INTEGER](INTEGER) value exceeds 32767, the value may become a negative value:
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```vb
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i% = 38000
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PRINT i%
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```
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```text
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-27536
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```
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> *Explanation:* Use an [_UNSIGNED](_UNSIGNED) [INTEGER](INTEGER) or a ~% variable type suffix for only positive integer values up to 65535.
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In **QB64**, [_UNSIGNED](_UNSIGNED) [INTEGER](INTEGER) values greater than 65535 cycle over again from zero:
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```vb
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i~% = 70000
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PRINT i~%
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```
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```text
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4464
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```
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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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Demonstrating how _UNSIGNED variables expand the [INTEGER](INTEGER) range.
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```vb
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DIM n AS _UNSIGNED INTEGER
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DIM pn AS _UNSIGNED INTEGER
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LOCATE 3, 6: PRINT "Press Esc to exit loop"
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FOR n = 1 TO 80000
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_LIMIT 10000 ' 6.5 second loop
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LOCATE 12, 37: PRINT n ' display current value
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IF n > 0 THEN pn = n ' find highest value
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IF n = 0 THEN Count = Count + 1: LOCATE 14, 37: PRINT "Count:"; Count; "Max:"; pn
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IF INP(&H60) = 1 THEN EXIT FOR ' escape key exit
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NEXT n
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END
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```
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```text
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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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```
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*Explanation:* The maximum value can only be 65535 (32767 + 32768) so the FOR loop repeats itself. Remove the [_UNSIGNED](_UNSIGNED) parts and run it again.
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## See Also
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* DECLARE, [SUB](SUB), [FUNCTION](FUNCTION)
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* [DIM](DIM), [_DEFINE](_DEFINE)
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* [DEFSTR](DEFSTR), [DEFLNG](DEFLNG), [DEFINT](DEFINT), [DEFSNG](DEFSNG), [DEFDBL](DEFDBL)
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* [INTEGER](INTEGER), [LONG](LONG), [_INTEGER64](_INTEGER64)
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* [ABS](ABS), [SGN](SGN)
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* [Variable Types](Variable-Types)
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