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(groff)Expressions

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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).  See below for
     the use of unary operators in motion requests.

   * Extrema: `>?' (maximum), `<?' (minimum).  For example, `5>?3'
     yields `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 work differently.  The `+' and `-' operators then indicate a
motion relative to the current position (down or up, respectively), and
the `|' operator indicates an absolute position on the page or input
line.  `+' and `-' are also treated differently by the following
requests and escapes: `bp', `in', `ll', `lt', `nm', `nr', `pl', `pn',
`po', `ps', `rt', `ti', `\R', and `\s'.  Here the plus and minus signs
indicate increments and decrements.

   Note: Setting Registers.

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

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