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_UNSIGNED

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PauloAstro edited this page Sep 5, 2022 · 6 revisions

[_UNSIGNED](_UNSIGNED defines a numerical value as being only positive.

Syntax

DIM variable AS [_UNSIGNED] datatype

_DEFINE letterRange AS [_UNSIGNED] datatype

Description

  • Datatype can be any of the following: INTEGER, LONG, _BIT, _BYTE, _INTEGER64, _OFFSET *SINGLE, DOUBLE and _FLOAT variable types cannot be _UNSIGNED.
  • _UNSIGNED can be used in a _DEFINE statement to set undefined variable name first letters as all positive-only values.
  • Can also be used in DIM statements or subprocedure parameter definitions following AS.
  • _UNSIGNED allows larger positive numerical variable value limits than signed ones.
  • The unsigned variable type suffix used is the tilde (~), right before the number's own type suffix: variableName~&

How negative values affect the _UNSIGNED value returned by a _BYTE (8 bits).



                        00000001 - unsigned & signed are both 1    
                        01111111 - unsigned & signed are both 127  
                        11111111 - unsigned is 255 but signed is -1
                        11111110 - unsigned is 254 but signed is -2
                        11111101 - unsigned is 253 but signed is -3

Example(s)

In QB64, when a signed INTEGER value exceeds 32767, the value may become a negative value:

i% = 38000
PRINT i% 


-27536

Explanation: Use an _UNSIGNED INTEGER or a ~% variable type suffix for only positive integer values up to 65535.

In QB64, _UNSIGNED INTEGER values greater than 65535 cycle over again from zero:

i~% = 70000
PRINT i~% 


 4464

Explanation: In QB64 an unsigned integer value of 65536 would be 0 with values increasing by the value minus 65536.

Demonstrating how _UNSIGNED variables expand the INTEGER range.

DIM n AS _UNSIGNED INTEGER
DIM pn AS _UNSIGNED INTEGER
LOCATE 3, 6: PRINT "Press Esc to exit loop"
FOR n = 1 TO 80000
  _LIMIT 10000 ' 6.5 second loop 
  LOCATE 12, 37: PRINT n ' display current value
  IF n > 0 THEN pn = n ' find highest value
  IF n = 0 THEN Count = Count + 1: LOCATE 14, 37: PRINT "Count:"; Count; "Max:"; pn
  IF INP(&H60) = 1 THEN EXIT FOR ' escape key exit
NEXT n
END 


   Press Esc to exit loop

                           65462

                          Count: 13 Max: 65535

Explanation: The maximum value can only be 65535 (32767 + 32768) so the FOR loop repeats itself. Remove the _UNSIGNED parts and run it again.

See Also

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