JavaScript/JScript: Control Structures I - Pearson Learning Solutions

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Chapter 14 JavaScript/JScript: Control Structures I 431
Operator Called Sample expression Explanation
++ preincrement ++a Increment a by 1, then use the new value of
a in the expression in which a resides.
++ postincrement a++ Use the current value of a in the expression
in which a resides, then increment a by 1.
-- predecrement --b Decrement b by 1, then use the new value
of b in the expression in which b resides.
-- postdecrement b-- Use the current value of b in the expression
in which b resides, then decrement b by 1.
Fig. 14.13 The increment and decrement operators.
Preincrementing (predecrementing) a variable causes the variable to be incremented
(decremented) by 1, then the new value of the variable is used in the expression in which it
appears. Postincrementing (postdecrementing) the variable causes the current value of the
variable to be used in the expression in which it appears, then the variable value is incremented
(decremented) by 1.
The script of Fig. 14.14 demonstrates the difference between the preincrementing version
and the postincrementing version of the ++ increment operator. Postincrementing the
variable c causes it to be incremented after it is used in the document.writeln method
call (line 14). Preincrementing the variable c causes it to be incremented before it is used
in the document.writeln method call (line 20). The program displays the value of c
before and after the ++ operator is used. The decrement operator (--) works similarly.
Good Programming Practice 14.10
For readability, unary operators should be placed next to their operands with no intervening
spaces. 14.10
1
2
3
4
5
6 Preincrementing and Postincrementing
7
8
9 var c;
10
11 c = 5;
12 document.writeln( "Postincrementing" );
13 document.writeln( c ); // print 5
14 document.writeln( "" + c++ ); // print 5 then increment
15 document.writeln( "" + c ); // print 6
16
Fig. 14.14 Differences between preincrementing and postincrementing (part 1 of 2).
e-Business and e-Commerce: How to Program, by Harvey M. Deitel, Paul J. Deitel, and Tem R. Nieto. Published by Prentice Hall.
Copyright © 2001 by Pearson Education, Inc.