(groff.info)Expressions

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5.3 Expressions
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`gtroff' has most arithmetic operators common to other languages:

   * Arithmetic: `+' (addition), `-' (subtraction), `/' (division), `*'
     (multiplication), `%' (modulo).

     `gtroff' only provides integer arithmetic.  The internal type used
     for computing results is `int', which is usually a 32bit signed
     integer.

   * Comparison: `<' (less than), `>' (greater than), `<=' (less than
     or equal), `>=' (greater than or equal), `=' (equal), `==' (the
     same as `=').

   * Logical: `&' (logical and), `:' (logical or).

   * Unary operators: `-' (negating, i.e. changing the sign), `+' (just
     for completeness; does nothing in expressions), `!' (logical not;
     this works only within `if' and `while' requests).(1) (Note:
     Expressions-Footnote-1)  See below for the use of unary
     operators in motion requests.

   * Extrema: `>?' (maximum), `<?' (minimum).

     Example:


          .nr x 5
          .nr y 3
          .nr z (\n[x] >? \n[y])

     The register `z' now contains 5.

   * Scaling: `(C;E)'.  Evaluate E using C as the default scaling
     indicator.  If C is missing, ignore scaling indicators in the
     evaluation of E.

   Parentheses may be used as in any other language.  However, in
`gtroff' they are necessary to ensure order of evaluation.  `gtroff'
has no operator precedence; expressions are evaluated left to right.
This means that `gtroff' evaluates `3+5*4' as if it were parenthesized
like `(3+5)*4', not as `3+(5*4)', as might be expected.

   For many requests which cause a motion on the page, the unary
operators `+' and `-' work differently if leading an expression.  They
then indicate a motion relative to the current position (down or up,
respectively).

   Similarly, a leading `|' operator indicates an absolute position.
For vertical movements, it specifies the distance from the top of the
page; for horizontal movements, it gives the distance from the beginning
of the _input_ line.

   `+' and `-' are also treated differently by the following requests
and escapes: `bp', `in', `ll', `lt', `nm', `nr', `pl', `pn', `po', `ps',
`pvs', `rt', `ti', `\H', `\R', and `\s'.  Here, leading plus and minus
signs indicate increments and decrements.

   Note: Setting Registers, for some examples.

 -- Escape: \B'anything'
     Return 1 if ANYTHING is a valid numeric expression; or 0 if
     ANYTHING is empty or not a valid numeric expression.

   Due to the way arguments are parsed, spaces are not allowed in
expressions, unless the entire expression is surrounded by parentheses.

   Note: Request and Macro Arguments, and Note: Conditionals and
Loops.