ASCII 35 — #

The number sign (also called hash, pound sign, or octothorpe) has an extraordinary range of uses across computing. In social media, it creates hashtags for content discovery and categorization. In programming, '#' starts comments in Python, Ruby, Perl, and shell scripts, and begins C/C++ preprocessor directives like #include and #define. In CSS, it introduces hexadecimal color codes (#FF0000) and ID selectors (#header). In URLs, '#' marks fragment identifiers. In Markdown, '#' creates headings. Few characters carry as many context-dependent meanings.

Symbol characters in ASCII include mathematical operators, logical notation, and special-purpose marks that serve critical roles across programming, mathematics, and digital communication. Symbols are heavily context-dependent — the same character may act as an arithmetic operator in one language, a regex metacharacter in another, and a shell configuration flag in a third context. This contextual polyvalence makes symbols among the most functionally overloaded characters in computing, requiring careful attention to their meaning in each domain.

In the ASCII encoding table, Number Sign is assigned code point 35 in decimal (0x23 hexadecimal, 043 octal, 00100011 binary). The 7-bit ASCII standard, first published in 1963 by the American Standards Association, defines exactly 128 characters that remain the foundation of text encoding systems worldwide. UTF-8, the dominant encoding on the modern web, is fully backward compatible with ASCII — every ASCII character is encoded as the identical single byte in UTF-8, guaranteeing that Number Sign works reliably across all operating systems, programming languages, and internet protocols.