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The name
"C sharp" was
inspired by musical notation where a sharp indicates that the written note should be made a
semitone higher in pitch.
This is similar to the language name of C++, where "++" indicates that a variable should be incremented by 1.
Due to technical limitations of display (standard fonts, browsers, etc.) and the fact that the sharp symbol
(U+266F ♯ music sharp sign (HTML: ♯))
is not present on the standard keyboard, the number sign
(U+0023 # number sign (HTML: #))
was chosen to represent the sharp symbol in the written name of the programming language.
This convention is reflected in the
ECMA-334 C# Language
Specification.
However, when it is practical to do so (for example, in advertising or in box art), Microsoft uses the intended musical symbol.