'''How can I do math in Tcl''' discusses `[expr]` and friends.



** See Also **

   [expr]:   A more detailed list of the functions that the man page skims over.

   [expr problems with int]:   Historical information regarding the previous ''long'' limitations of numbers in Tcl, and a discussion on ''wide''.



** Description **

`[expr]` is the primary tool for doing calculations in Tcl.

Prior to [Changes in Tcl/Tk 8.5%|%Tcl 8.5], built-in math operations were [expr
problems with int%|%limited] to numbers that could be stored in as a [C]
''long'' or ''double''.  To perform math on longer numbers an some alternative
like [Tom Poindexter%|%TomPoindexter's] [mpexpr] extension was needed.

[DKF]:  From Tcl 8.4 onwards, you can also use a larger integer type termed a
''wide''.  This lets you work with 64-bit values on 32-bit machines...

Unless you have a ''very'' good reason not to, you should always [Brace your
expr-essions%|%pass a literal value] to `[expr]` so that Tcl can parse
[bytecode%|%compile] and compile it just once.

[AM]:  A "very good reason" is that part or whole of the expression is not a
constant, e.g.

======
set v [expr "$a $op $b"]
======

Surrounding this epression with braces would fail because the literal value `$a
$op $b` is not a syntactictally-correct expression.


<<categories>> Command | Mathematics