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(gawk.info)Arithmetic Ops

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Arithmetic Operators
====================

   The `awk' language uses the common arithmetic operators when
evaluating expressions.  All of these arithmetic operators follow normal
precedence rules and work as you would expect them to.

   The following example uses a file named `grades', which contains a
list of student names as well as three test scores per student (it's a
small class):

     Pat   100 97 58
     Sandy  84 72 93
     Chris  72 92 89

This programs takes the file `grades' and prints the average of the
scores:

     $ awk '{ sum = $2 + $3 + $4 ; avg = sum / 3
     >        print $1, avg }' grades
     -| Pat 85
     -| Sandy 83
     -| Chris 84.3333

   The following list provides the arithmetic operators in `awk', in
order from the highest precedence to the lowest:

`- X'
     Negation.

`+ X'
     Unary plus; the expression is converted to a number.

`X ^ Y'
`X ** Y'
     Exponentiation; X raised to the Y power.  `2 ^ 3' has the value
     eight; the character sequence `**' is equivalent to `^'.

`X * Y'
     Multiplication.

`X / Y'
     Division;  because all numbers in `awk' are floating-point
     numbers, the result is _not_ rounded to an integer--`3 / 4' has
     the value 0.75.  (It is a common mistake, especially for C
     programmers, to forget that _all_ numbers in `awk' are
     floating-point, and that division of integer-looking constants
     produces a real number, not an integer.)

`X % Y'
     Remainder; further discussion is provided in the text, just after
     this list.

`X + Y'
     Addition.

`X - Y'
     Subtraction.

   Unary plus and minus have the same precedence, the multiplication
operators all have the same precedence, and addition and subtraction
have the same precedence.

   When computing the remainder of `X % Y', the quotient is rounded
toward zero to an integer and multiplied by Y. This result is
subtracted from X; this operation is sometimes known as "trunc-mod."
The following relation always holds:

     b * int(a / b) + (a % b) == a

   One possibly undesirable effect of this definition of remainder is
that `X % Y' is negative if X is negative.  Thus:

     -17 % 8 = -1

   In other `awk' implementations, the signedness of the remainder may
be machine dependent.

   *Note:* The POSIX standard only specifies the use of `^' for
exponentiation.  For maximum portability, do not use the `**' operator.