Latin Capital Letter A
Sitting at ASCII code point 65 (0x41), uppercase 'A' marks the start of the Latin letter range in the ASCII table. It is the first letter of the Latin alphabet and, as a hexadecimal digit, represents the value 10, appearing in color codes, memory addresses, and hash digests. Beyond computing, 'A' is the SI symbol for the ampere and names the universal tuning pitch for Western instruments. Its lowercase counterpart 'a' at 97 (0x61) lies 32 code points above — a single-bit difference enabling efficient case conversion.
Technical Details
Code Example
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char c = 'A';int index = c - 'A'; // Standard idiom to map uppercase char to 0-25 index// index == 0
Common Usage
Hexadecimal digit: Uppercase 'A' through 'F' represent values 10–15 in hexadecimal notation. Most hex parsers treat 'A' and 'a' as equivalent, though conventions vary — RFC 4122 (UUIDs) recommends lowercase, while many debug tools, memory inspectors, and Intel-style assembly listings default to uppercase.
SI unit and music standard: In the International System of Units, 'A' is the symbol for the ampere, one of the seven SI base units and the standard measure of electric current — making it arguably the single most consequential real-world meaning of the character. In Western music, A4 (A above middle C, tuned to 440 Hz) serves as the universal reference pitch against which orchestras and instruments are tuned, a standard formalized by ISO 16 in 1975.
Typography and glyph anatomy: Uppercase 'A' is one of the most structurally distinctive capital letters, formed by two diagonal strokes meeting at an apex with a horizontal crossbar. Typographic variations — crossbar height, apex treatment (pointed, flat, or notched), and stroke contrast — are often among the first details type designers adjust to establish a typeface's visual identity.
Diacritical variants: Uppercase 'A' carries the same broad family of diacritical forms as its lowercase counterpart — À, Á, Â, Ä, Å, Ã, Ą, and others. In languages such as Swedish and Danish, Å functions as a separate letter sorted after Z in the alphabet, while in French and Portuguese, À and à are accented variants of the base letter that do not alter alphabetical position.
Hexadecimal digit: Uppercase 'A' through 'F' represent values 10–15 in hexadecimal notation. Most hex parsers treat 'A' and 'a' as equivalent, though conventions vary — RFC 4122 (UUIDs) recommends lowercase, while many debug tools, memory inspectors, and Intel-style assembly listings default to uppercase.
SI unit and music standard: In the International System of Units, 'A' is the symbol for the ampere, one of the seven SI base units and the standard measure of electric current — making it arguably the single most consequential real-world meaning of the character. In Western music, A4 (A above middle C, tuned to 440 Hz) serves as the universal reference pitch against which orchestras and instruments are tuned, a standard formalized by ISO 16 in 1975.
Typography and glyph anatomy: Uppercase 'A' is one of the most structurally distinctive capital letters, formed by two diagonal strokes meeting at an apex with a horizontal crossbar. Typographic variations — crossbar height, apex treatment (pointed, flat, or notched), and stroke contrast — are often among the first details type designers adjust to establish a typeface's visual identity.
Diacritical variants: Uppercase 'A' carries the same broad family of diacritical forms as its lowercase counterpart — À, Á, Â, Ä, Å, Ã, Ą, and others. In languages such as Swedish and Danish, Å functions as a separate letter sorted after Z in the alphabet, while in French and Portuguese, À and à are accented variants of the base letter that do not alter alphabetical position.