File: gawk.info,  Node: Arithmetic Ops,  Next: Concatenation,  Up: All Operators

6.2.1 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 program 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 ^ Y'
'X ** Y'
     Exponentiation; X raised to the Y power.  '2 ^ 3' has the value
     eight; the character sequence '**' is equivalent to '^'.  (c.e.)

'- X'
     Negation.

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

'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

This definition is compliant with the POSIX standard, which says that
the '%' operator produces results equivalent to using the standard C
'fmod()' function, and that function in turn works as just described.

   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.