C Programming Language Bill Jensen CS 354 May, 3 rd 2007

Catalyst Ken Thompson wanted a comfortable computing environment of his own design. B programming language was created, based on languages used when creating Multics; especially BCPL. Thompson decided Unix needed a system programming language. In late 1960’s Bell Labs left project on Multics, and soon after he and others began working on the Unix Operating System.

Creation By 1970 Unix had shown promise and Bell Labs acquired the new DEC PDP-11 By 1971…We all wanted to create interesting software more easily. B’s problems – 1) Clumsy Character handling 2) Floating point not available on PDP-11 3) Implied overhead with pointers Alterations to B and a new name, NB.

Creation - continued NB proved to be insufficient and with further changes was renamed to C. Many changes around , but main was introduction of preprocessor. Portability developed as I/O Libraries written by Mike Lesk produced changes focused on portability and type safety Brian Kernighan and Dennis Ritchie Published The C Programming Language.

Control - standardization Portability tests (Interdata 8/32, DEC VAX 11/780) lead to wide spread use during the 1980’s. Compilers became available on most every machine architecture. Wide use, including use on commercial and Government projects lead to establishment of X3J11 committee established by ANSI to produce a standardization of C.

Characteristics An Imperative, Procedural programming language. Design based on the implementation of computer processors based upon the von Neumann architecture. Low level access to memory by machine addresses and typed pointers.

Variables, Types & Operators Variables - Must begin with letter followed by any number and combination of letters and digits. (strings are implemented as char arrays) Types – char, int (short, long), float, double shorts, ints – min 16 bits Long – min 32 bits Binary Operators: +, -, *, /, % Logic Operators: >, >=, <, <=, ==, !=, &&, ||, ! (negate) Bitwise: &, |, ^, >, - (unary)

Assignment Expressions Assignment: =, +=, -=, *=, /=, &=, ^=, |=, >= Most associativity is Left to Right Ex. x = 1 + 2; Ex. y += 4; (y = y + 4;)

Control Flow If-Else, Else-If, Switch, Loops, GOTO Loops – While, For, Do-while GOTO and Labels – GOTO’s can be useful in error handling in special cases but usually should be avoided Labels – same form as a variable followed by a colon “goto statements should be used rarely, it at all” – Kernighan, Ritchie

Pointers and Arrays Pointers contain addresses of variables. Ex. int x = 10; // var x has value of 10 int *ptr; // ptr points to the address of an int ptr = &x; // ptr now has value of x (10) Arrays can be declared normally and as pointer arrays. Ex. Int array[] // one dimensional int twoDimArray[][] // two dimensional array * Pointer arrays are usually faster but harder to understand.

Structures Structures – a collection of one or more variables or any type. Structures are used to help organize complicated data. Ex. Struct account { char *accountHolder; double checkingBalance; double savingsBalance; }

Conclusion Readability – overall easy to read and intuitive. Pointers can make reading code difficult. Simplicity – simple design making c easy to learn and apply. Orthogonality – c is not very restrictive, which allows some creativity and some higher chances of writing bugged code.

Conclusion - continued Easy to learn basic concepts. Lack simple implementation of object oriented programming can make class OOP tedious.

Primary Uses True to its original purpose C is most often used in systems programming. Operating Systems Embedded Systems Intermediate Language for higher-level languages * Java Computer Game Programming

Bibliography Kernighan, Brian W., and Dennis M. Ritchie. The C Programming Language. New Jersey: Prentice Hall, Sebesta, Robert W. Concepts of programming languages. Boston: Pearson, Ritchie, Dennis M. The Development of the C Language*. Murray Hill, NJ:. "C (programming language)." wikipedia.org. April, 25 th