C/the.ansi.c.programming.language/c.programming.notes/sx7.html

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   9 <title>Chapter 7: More Operators</title>
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  15 <H1>Chapter 7: More Operators</H1>
  16
  17 <p>In this chapter we'll meet some
  18 (though still not all)
  19 of C's more advanced arithmetic operators.
  20 The ones we'll meet here have to do with making common patterns of
  21 operations easier.
  22 </p><p>It's extremely common in programming to have to
  23 <dfn>increment</dfn> a variable by 1, that is, to add 1 to it.
  24 (For example, if you're processing each element of an array,
  25 you'll typically write a loop with an index or pointer variable
  26 stepping through the elements of the array,
  27 and you'll increment the variable each time through the loop.)
  28 The classic way to increment a variable is with an assignment like
  29 <pre>
  30         i = i + 1
  31 </pre>
  32 Such an assignment is perfectly common and acceptable, but it
  33 has a few slight problems:
  34 <OL><li>As we've mentioned, it looks a little odd,
  35 especially from an algebraic perspective.
  36 <li>If the object being incremented is
  37 not a simple variable,
  38 the idiom can become cumbersome to type,
  39 and correspondingly more error-prone.
  40 For example, the expression
  41 <pre>
  42         a[i+j+2*k] = a[i+j+2*k] + 1
  43 </pre>
  44 is a bit of a mess,
  45 and you may have to look closely to see that the
  46 similar-looking
  47 expression
  48 <pre>
  49         a[i+j+2*k] = a[i+j+2+k] + 1
  50 </pre>
  51 probably has
  52 a mistake in it.
  53 <li>Since incrementing
  54 things
  55
  56 is <em>so</em> common,
  57 it might be nice to have an easier way of doing it.
  58 </OL>In fact,
  59 C provides not one but two other,
  60 simpler ways of incrementing
  61 variables
  62 and
  63 performing other
  64 similar
  65 operations.
  66 </p><p><a href="sx7a.html" rel=subdocument>7.1 Assignment Operators</a></p>
  67 <p><a href="sx7b.html" rel=subdocument>7.2 Increment and Decrement Operators</a></p>
  68 <p><a href="sx7c.html" rel=subdocument>7.3 Order of Evaluation</a></p>
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  78 This page by <a href="http://www.eskimo.com/~scs/">Steve Summit</a>
  79 // <a href="copyright.html">Copyright</a> 1995-1997
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