'''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 **

Prior to 8.5, [Tcl]'s built in math support was [expr problems with
int%|%limited] to what will fit into a ''long'' or ''double'' [C] variable type.  To
perform math on longer numbers, some alternative, such as [Tom Poindexter]'s
[mpexpr] extension, were 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...

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

Unless you have a ''very'' good reason not to, you should always [Brace your
expr-essions%|%enclose the argument expression] to [[expr]] in curly braces.
This allows the bytecode compiler to optimise your code more thoroughly since
it has fewer possible interpretations and the contents of variables and the
results of commands will not unexpectedly modify the meaning of the expression.

[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, since `$a $op $b` is not a
properly formed expression.


<<categories>> Command | Mathematics