C is the third letter in the Latin alphabet. C or c may also refer to: Computing C (programming language), developed at Bell Labs in 1972 C, a hexadecimal digit C, a computable function, the set of all computable decision problems C:, or "Drive C", the default drive letter assignment for the default hard drive in DOS and Windows Measurement °C, Celsius temperature scale Carat (purity) centi-, an SI prefix Coulomb, the SI derived unit for electric charge Cup (unit), a unit of volume Science Troponin C, one of the three troponins Carbon, symbol C, a chemical element Atomic carbon or C ATC code C or cardiovascular system, a section of the Anatomical Therapeutic Chemical Classification System Haplogroup C (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup Haplogroup C-M130 (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup once called simply C Cytosine, nucleic acid C (or Cys), an abbreviation for the amino acid cysteine C, a prefix for astronomical objects listed in the Caldwell catalogue, ranging from C1 to C109 C, a prefix for astronomical star clusters, which follow the IAU's "Chhmm±ddd" format c, the speed of light in vacuum c, the speed of sound c, the specific heat capacity of a substance c, any constant C, capacitance C, symbol of coulomb Charm quark () C-value, DNA contained within a haploid nucleus Technology C battery, a size of battery Capacitor or C C battery, a type of battery for vacuum tube radios C or C-rate, a rate of charge and discharge of a battery Mathematics C, a digit meaning twelve in hexadecimal and other positional numeral systems with a radix of 13 or greater C, the constant of integration C, in Roman numerals, the symbol for 100 C, ℂ, or , the set of all complex numbers ℭ or , the cardinality of the continuum C, the set of continuous functions The combination or "choose" function c space, the space of all convergent sequences in functional analysis Music C (musical note), and keys based on it: C major C minor C Album, an album by Kinki Kids C major chord, a chord in popular music , symbol used to designate common time , symbol used to designate alla breve "C", a composition by Francis Poulenc, one of Deux Poèmes de Louis Aragon Literature C (novel), a novel by Tom McCarthy C, a 1924 novel by Maurice Baring C Magazine, a magazine published by