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   9 <title>2.5 Arithmetic Operators</title>
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  15 <H2>2.5 Arithmetic Operators</H2>
  16
  17 <p>[This section corresponds to K&amp;R Sec. 2.5]
  18 </p><p>The basic operators for performing arithmetic are the same in
  19 many computer languages:
  20 <br>
  21 <br>
  22 <pre>
  23         <TT>+</TT>      addition
  24         <TT>-</TT>      subtraction
  25         <TT>*</TT>      multiplication
  26         <TT>/</TT>      division
  27         <TT>%</TT>      modulus (remainder)
  28 </pre>
  29 </p><p>
  30 The <TT>-</TT> operator can be used in two ways:
  31 to subtract two numbers
  32 (as in <TT>a - b</TT>),
  33 or to negate one number
  34 (as in <TT>-a + b</TT> or <TT>a + -b</TT>).
  35 </p><p>When applied to integers,
  36 the division operator <TT>/</TT> discards any remainder,
  37 so <TT>1 / 2</TT> is 0
  38 and <TT>7 / 4</TT> is 1.
  39 But when either operand is a floating-point quantity
  40 (type <TT>float</TT> or <TT>double</TT>),
  41 the division operator yields a floating-point result,
  42 with a potentially nonzero fractional part.
  43 So <TT>1 / 2.0</TT> is 0.5,
  44 and <TT>7.0 / 4.0</TT> is 1.75.
  45 </p><p>The <dfn>modulus</dfn> operator <TT>%</TT> gives you the
  46 remainder
  47 when two integers are divided:
  48 <TT>1 % 2</TT> is 1;
  49 <TT>7 % 4</TT> is 3.
  50 (The modulus operator can only be applied to integers.)
  51 </p><p>An additional arithmetic operation you might be wondering about
  52 is exponentiation.
  53 Some languages have an exponentiation operator
  54 (typically <TT>^ or </TT><TT>**</TT>),
  55 but C doesn't.
  56 (To square or cube a number,
  57 just multiply it by itself.)
  58 </p><p>Multiplication, division, and modulus all have higher
  59 <dfn>precedence</dfn> than addition and subtraction.
  60 The term ``precedence'' refers to how ``tightly'' operators bind to
  61 their operands (that is, to the things they operate on).
  62 In mathematics, multiplication has higher precedence than
  63 addition, so <TT>1 + 2 * 3</TT> is 7, not 9.
  64 In other words, <TT>1 + 2 * 3</TT> is equivalent to <TT>1 + (2 * 3)</TT>.
  65 C is the same way.
  66 </p><p>All of these operators ``group'' from left to right,
  67 which means that
  68 when two or
  69 more of them have the same precedence and participate next to each
  70 other in an expression,
  71 the evaluation conceptually proceeds from left to right.
  72 For example,
  73 <TT>1 - 2 - 3</TT> is equivalent to <TT>(1 - 2) - 3</TT>
  74 and gives -4, not +2.
  75 (``Grouping'' is sometimes called <dfn>associativity</dfn>,
  76 although the term is used somewhat differently in programming
  77 than it is in mathematics.
  78 Not all C operators group from left to right;
  79 a few group from right to left.)
  80 </p><p>Whenever the default precedence or associativity
  81 doesn't give you the grouping you want,
  82 you can always
  83 use explicit parentheses.
  84 For example,
  85 if you wanted to add 1 to 2 and then multiply the result by 3,
  86 you could write <TT>(1 + 2) * 3</TT>.
  87 </p><p>By the way,
  88 the word ``arithmetic''
  89 as used in the title of this section
  90 is an adjective, not a noun,
  91 and it's pronounced differently than the noun:
  92 the accent is on the third syllable.
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