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counters, counting, increment, and decrement
summary
This subchapter looks at counters, counting, incrementing, and decrementing.
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This subchapter looks at counters, counting, incrementing, and decrementing.
free computer programming text book projecttable of contents
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This subchapter is a stub section. It will be filled in with instructional material later. For now it serves the purpose of a place holder for the order of instruction.
Professors are invited to give feedback on both the proposed contents and the propsed order of this text book. Send commentary to Milo, PO Box 1361, Tustin, California, 92781, USA.
This subchapter looks at counters, counting, incrementing, and decrementing.
005010 ADD 1 TO LINE-COUNT.
The example increments (adds one to) the variable LINE-COUNT.
ADD1(x) — LISP function that takes one argument of type fixed or float and increments the value.
An integer variable may be incremented by either of the following assignment statements:
$i = $i + 1;
-OR-
$i++;
Stanford CS Education Library This [the following section until marked as end of Stanford University items] is document #101, Essential C, in the Stanford CS Education Library. This and other educational materials are available for free at http://cslibrary.stanford.edu/. This article is free to be used, reproduced, excerpted, retransmitted, or sold so long as this notice is clearly reproduced at its beginning. Copyright 1996-2003, Nick Parlante, nick.parlante@cs.stanford.edu.
C includes the usual binary and unary arithmetic operators. See the appendix for the table of precedence. [Found in this book in the subchapter on order of precedence]
The unary ++ and -- operators increment or decrement the value in a variable. There are “pre” and “post” variants for both operators which do slightly different things (explained below)
var++ increment “post” variant ++var increment “pre” variant var-- decrement “post” variant --var decrement “pre” variant
int i = 42;
i++; // increment on i
// i is now 43
i--; // decrement on i
// i is now 42
The Pre/Post variation has to do with nesting a variable with the increment or decrement operator inside an expression -- should the entire expression represent the value of the variable before or after the change? I never use the operators in this way (see below), but an example looks like…
int i = 42;
int j;
j = (i++ + 10);
// i is now 43
// j is now 52 (NOT 53)
j = (++i + 10)
// i is now 44
// j is now 54
Relying on the difference between the pre and post variations of these operators is a classic area of C programmer ego showmanship. The syntax is a little tricky. It makes the code a little shorter. These qualities drive some C programmers to show off how clever they are. C invites this sort of thing since the language has many areas (this is just one example) where the programmer can get a complex effect using a code which is short and dense.
If I want j to depend on i’s value before the increment, I write…
j = (i + 10);
i++;
Or if I want to j to use the value after the increment, I write…
i++;
j = (i + 10);
Now then, isn’t that nicer? (editorial) Build programs that do something cool rather than programs which flex the language’s syntax. Syntax -- who cares?
Stanford CS Education Library This [the above section] is document #101, Essential C, in the Stanford CS Education Library. This and other educational materials are available for free at http://cslibrary.stanford.edu/. This article is free to be used, reproduced, excerpted, retransmitted, or sold so long as this notice is clearly reproduced at its beginning. Copyright 1996-2003, Nick Parlante, nick.parlante@cs.stanford.edu.
For most processors, integer arithmetic is faster than floating point arithmetic. This can be reversed in special cases such digital signal processors.
The basic four integer arithmetic operations are addition, subtraction, multiplication, and division. Arithmetic operations can be signed or unsigned (unsigned is useful for effective address computations). Some older processors don’t include hardware multiplication and division. Some processors don’t include actual multiplication or division hardware, instead looking up the answer in a massive table of results embedded in the processor.
A specialized, but common, form of addition is an increment instruction, which adds one to the contents of a register or memory location. For address computations, “increment” may mean the addition of a constant other than one. Some processors have “short” or “quick” addition instructions that extend increment to include a small range of positive values.
A specialized, but common, form of subtraction is an decrement instruction, which subtracts one from the contents of a register or memory location. For address computations, “decrement” may mean the subtraction of a constant other than one. Some processors have “short” or “quick” subtraction instructions that extend decrement to include a small range of values.
See also Integer Arithmetic Instructions in Assembly Language
Coding example: I am making heavily documented and explained open source code for a method to play music for free — almost any song, no subscription fees, no download costs, no advertisements, all completely legal. This is done by building a front-end to YouTube (which checks the copyright permissions for you).
View music player in action: www.musicinpublic.com/.
Create your own copy from the original source code/ (presented for learning programming).
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