Temporary variable
In computer programming, a temporary variable is a variable whose purpose is short-lived, usually to hold temporarily data that will soon be discarded, or before it can be placed at a more permanent memory location. Because it is short-lived, it is usually declared with local scope. There is no formal definition of what makes a variable temporary, but it is an often–used term in programming.
A typical example would be that of swapping the contents of two variables. To swap the contents of variables a and b one would typically use a temporary variable temp as follows, so as to preserve the data from a as it is being overwritten by b:
temp := a a := b b := temp
A more real example is that of swapping two elements in an array, as is done in the RC4 algorithm and in sorting algorithms.
When programming at the assembly level, it may be possible, depending on the available instruction set, to swap two values without the explicit use of a third temporary variable. For example, in the more recent Intel assemblies the XCHG operation performs a swap in one line of code, rather than three, and without the need of the programmer naming a temporary register or variable. (But this does not necessarily lead to a performance improvement, since the same three-step process has to be performed within the processor, effectively using another three-step process where a register plays the role of the temporary variable.)
Temporary variables are usually named with identifiers that abbreviate the word temporary, such as temp, tmp or simply t, or with common metasyntactic variable names, the most common of which are foo, bar, baz (See also foobar).