Increment Operators
===================

   "Increment operators" increase or decrease the value of a variable
by 1.  You could do the same thing with an assignment operator, so the
increment operators add no power to the `awk' language; but they are
convenient abbreviations for something very common.

   The operator to add 1 is written `++'.  It can be used to increment
a variable either before or after taking its value.

   To pre-increment a variable V, write `++V'.  This adds 1 to the
value of V and that new value is also the value of this expression.
The assignment expression `V += 1' is completely equivalent.

   Writing the `++' after the variable specifies post-increment.  This
increments the variable value just the same; the difference is that the
value of the increment expression itself is the variable's *old* value.
Thus, if `foo' has the value 4, then the expression `foo++' has the
value 4, but it changes the value of `foo' to 5.

   The post-increment `foo++' is nearly equivalent to writing `(foo +=
1) - 1'.  It is not perfectly equivalent because all numbers in `awk'
are floating point: in floating point, `foo + 1 - 1' does not
necessarily equal `foo'.  But the difference is minute as long as you
stick to numbers that are fairly small (less than a trillion).

   Any lvalue can be incremented.  Fields and array elements are
incremented just like variables.  (Use `$(i++)' when you wish to do a
field reference and a variable increment at the same time.  The
parentheses are necessary because of the precedence of the field
reference operator, `$'.)

   The decrement operator `--' works just like `++' except that it
subtracts 1 instead of adding.  Like `++', it can be used before the
lvalue to pre-decrement or after it to post-decrement.

   Here is a summary of increment and decrement expressions.

`++LVALUE'
     This expression increments LVALUE and the new value becomes the
     value of this expression.

`LVALUE++'
     This expression causes the contents of LVALUE to be incremented.
     The value of the expression is the *old* value of LVALUE.

`--LVALUE'
     Like `++LVALUE', but instead of adding, it subtracts.  It
     decrements LVALUE and delivers the value that results.

`LVALUE--'
     Like `LVALUE++', but instead of adding, it subtracts.  It
     decrements LVALUE.  The value of the expression is the *old* value
     of LVALUE.