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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
lvalue++
--lvalue
++lvalue, but instead of adding, it subtracts. It
decrements lvalue and delivers the value that results.
lvalue--
lvalue++, but instead of adding, it subtracts. It
decrements lvalue. The value of the expression is the old
value of lvalue.
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