Empty string

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The empty string is the unique string of no characters over some alphabet Σ, and is denoted ε or λ. The length of this empty string is 0.

Under concatenation, the empty string is the identity element of the free monoid on Σ. That is, for any string s, sε = εs = s.

[edit] Representations

In many programming languages, the empty string is denoted with two double quotes: "" The empty string is also sometimes noted by the Greek letter λ.

[edit] Implementation

In C, empty strings is represented by a character array with a null character in the zeroeth position.