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   9 <title>2.7 Function Calls</title>
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  15 <H2>2.7 Function Calls</H2>
  16
  17 <p>We'll have much more to say about functions in a later chapter,
  18 but for now let's just look at how they're called.
  19 (To review: what a function <em>is</em> is a piece of code,
  20 written by you or by someone else, which
  21 performs some useful, compartmentalizable task.)
  22 You call a function by mentioning its name followed by a pair
  23 of parentheses.
  24 If the function takes any arguments, you place the arguments
  25 between the parentheses, separated by commas.
  26 These are all function calls:
  27 <pre>
  28         printf("Hello, world!\n")
  29         printf("%d\n", i)
  30         sqrt(144.)
  31         getchar()
  32 </pre>
  33 The arguments to a function can be arbitrary expressions.
  34 Therefore, you don't have to say things like
  35 <pre>
  36         int sum = a + b + c;
  37         printf("sum = %d\n", sum);
  38 </pre>
  39 if you don't want to;
  40 you can instead collapse it to
  41 <pre>
  42         printf("sum = %d\n", a + b + c);
  43 </pre>
  44 Many functions return values, and when they do, you can embed
  45 calls to these functions within larger expressions:
  46 <pre>
  47         c = sqrt(a * a + b * b)
  48         x = r * cos(theta)
  49         i = f1(f2(j))
  50 </pre>
  51 The first expression squares <TT>a</TT> and <TT>b</TT>,
  52 computes the square root of the sum of the squares,
  53 and assigns the result to <TT>c</TT>.
  54 (In other words,
  55 it computes <TT>a * a + b * b</TT>,
  56 passes that number to the <TT>sqrt</TT> function,
  57 and assigns <TT>sqrt</TT>'s return value to <TT>c</TT>.)
  58 The second expression passes the value of the variable <TT>theta</TT> to
  59 the <TT>cos</TT> (cosine) function,
  60 multiplies the result by <TT>r</TT>,
  61 and assigns the result to <TT>x</TT>.
  62 The third expression
  63 passes the value of the variable <TT>j</TT> to the function <TT>f2</TT>,
  64 passes the return value of <TT>f2</TT>
  65 immediately to the function <TT>f1</TT>,
  66 and finally assigns <TT>f1</TT>'s return value to the variable <TT>i</TT>.
  67 </p><hr>
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  76 This page by <a href="http://www.eskimo.com/~scs/">Steve Summit</a>
  77 // <a href="copyright.html">Copyright</a> 1995-1997
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