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Topic: Just Thought I'd Mention... (Read 744 times) |
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Matt
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Just Thought I'd Mention...
« Thread started on: Sep 20th, 2010, 05:39am » |
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Reviewing another program someone had written, I found a little trick that I didn't know existed. It's a bonus with the +=, -=, etc. The use of it I have known since starting work with BB4W. But what I've just discovered is quite useful.
Original BBC Basic:
Code:(1.) VARIABLE% = VARIABLE% + CONSTANT
BB4W:
Code:(1.) VARIABLE% = VARIABLE% + CONSTANT
(2.) VARIABLE% += CONSTANT
Now, if VARIABLE% didn't exist in the first place command (1.) would error. However, command (2.) does not. This is useful when closing a window, for instance.
Code:VARIABLE% += 0: IF VARIABLE% THEN [close window]
Just thought I'd mention it. Well done Richard.
I know there must be thousands of other useful bonuses in the change from BBC Basic to BB4W, but I also wondered whether anyone else knew of anything little like this. Or is this just opening a whole box of bicuits?
Matt
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admin
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Re: Just Thought I'd Mention...
« Reply #1 on: Sep 20th, 2010, 08:21am » |
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on Sep 20th, 2010, 05:39am, Matt wrote: Code:VARIABLE% += 0: IF VARIABLE% THEN [close window]
Just thought I'd mention it. |
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Yes, many of my programs use that technique in their PROCcleanup routines. For example this in cpuspeed.bbc:
Code: DEF PROCcleanup
pCPU% += 0 : IF pCPU% SYS !(!pCPU%+8), pCPU% : pCPU% = 0
pEnum% += 0 : IF pEnum% SYS !(!pEnum%+8), pEnum% : pEnum% = 0
pSvc% += 0 : IF pSvc% SYS !(!pSvc%+8), pSvc% : pSvc% = 0
pLoc% += 0 : IF pLoc% SYS !(!pLoc%+8), pLoc% : pLoc% = 0
SYS `CoUninitialize`
ENDPROC
It's specifically documented in the Wiki here:
http://bb4w.wikispaces.com/Forcing+a+variable+to+exist
Richard.
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knudvaneeden
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Re: Just Thought I'd Mention...
« Reply #2 on: Sep 20th, 2010, 12:41pm » |
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on Sep 20th, 2010, 05:39am, Matt wrote:Reviewing another program someone had written, I found a little trick that I didn't know existed. It's a bonus with the +=, -=, etc. The use of it I have known since starting work with BB4W. But what I've just discovered is quite useful.
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This shorthand notation +=, *=, ... exists since 1969.
Ken Thompson and Dennis Ritchie of Bell Labs introduced it in their C language.
Nowadays used in several other computer languages, like C++, and also BBCBasic for Windows.
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knudvaneeden
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Re: Just Thought I'd Mention...
« Reply #3 on: Sep 20th, 2010, 1:15pm » |
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Because C was a successor of e.g. the earlier B language, I checked if it maybe existed earlier than 1969, and found:
"Compound assignment operators, such as a += b to “add b to a” were popularized by the C and Pascal, but first available in ALGOL 68"
http://hhh.gavilan.edu/dvantassel/history/assignment.html#_Toc123623884
So it must have been used since about 1968.
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admin
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Re: Just Thought I'd Mention...
« Reply #4 on: Sep 20th, 2010, 4:28pm » |
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on Sep 20th, 2010, 12:41pm, knudvaneeden wrote:| This shorthand notation +=, *=, ... exists since 1969. |
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I don't think the OP was commenting on the existence or function of the += operator, but the fact that it can be used to create a variable. Just because other languages have the same operator it doesn't follow that it will have that behaviour.
Incidentally, BBC BASIC didn't have the += operator (and friends) until version 5, in around 1986.
Richard.
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| « Last Edit: Sep 20th, 2010, 4:37pm by admin » |
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