### 12.1 Decrement and increment operators ¶

Increment and decrement of integers are supported using the builtins `incr` and `decr`:

Builtin: incr (number) ¶
Builtin: decr (number) ¶

  Expand to the numerical value of number, incremented or decremented, respectively, by one. Except for the empty string, the expansion is empty if number could not be parsed.

  The macros `incr` and `decr` are recognized only with parameters.

    incr(`4')
    ⇒5
    decr(`7')
    ⇒6
    incr()
    error→m4:stdin:3: empty string treated as 0 in builtin `incr'
    ⇒1
    decr()
    error→m4:stdin:4: empty string treated as 0 in builtin `decr'
    ⇒-1