Encyclopedia of Computer Science and Technology

CCThe C programming language was developed in the early1970s by Dennis Ritchie, who based it on the earlier languagesBCPL and B. C was first used on DEC PDP-11computers running the newly developed UNIX operatingsystem, where the language provided a high-level alternativeto the use of PDP Assembly language for developmentof the many utilities that give UNIX its flexibility.Since the 1980s, C and its descendent, C++, have becomethe most widely used programming languages.Language FeaturesLike the earlier Algol and the somewhat later Pascal, Cis a procedural language that reflects the philosophy ofprogramming that was gradually taking shape duringthe 1970s (see structured programming). In general,C’s approach can be described as providing the necessaryfeatures for real world computing in a compact andefficient form. The language provides the basic controlstructures such as if and switch (see branching statements)and while, do, and for (see loop). The built-indata types provide for integers (int, short, and long),floating-point numbers (float and double), and characters(char). An array of any type can be declared, and a stringis implemented as an array of char (see data types andcharacters and strings).Pointers (references to memory locations) are used for avariety of purposes, such as for storing and retrieving datain an array (see pointers and indirection). While theuse of pointers can be a bit difficult for beginners to understand,it reflects C’s emphasis as a systems programminglanguage that can “get close to the hardware” in manipulatingmemory.Data of different types can be combined into a recordtype called a struct. Thus, for example:struct Employee_Record {char [10] First_Name;char [1] Middle_Initial;char [20] Last_Name;int Employee_Number;} ;(There is also a union, which is a struct where the samestructure can contain one of two different data items.)The standard mathematical and logical comparisonoperators are available. There are a couple of quirks: theequals comparison operator is = =, while a single equal sign= is an assignment operator. This can create a pitfall for thewary, since the conditionif (Total = 10)printf (“Finished!”);always prints Finished, since the assignment Total = 10returns a value of 10 (which not being zero, is “true” andsatisfies the if condition).C also features an increment ++ and decrement - - operator,which is convenient for the common operation of raisingor lowering a variable by one in a counting loop. In Cthe following statements are equivalent:65