History of C Language and UNIX

History of C Language

• C language evolved from ALGOL, which was the first language to use a block structure (introduced in 1960).
• BCPL, derived from ALGOL, was developed in 1967.
• Ken Thompson created the B language, using BCPL, in 1970, both BCPL and B were typeless.
• Dennis Ritchie developed C using BCPL and B at Bell Labs in 1972.
• C's popularity increased with the release of C compilers for commercial use, as well as the increasing popularity of UNIX.

History of UNIX

• Ken Thompson and Dennis Ritchie designed a file system for Bell Labs in 1969 to provide a more convenient programming environment.
• This file system evolved into an early version of the UNIX Operating System.
• The system was implemented on a PDP-7 (in 1971) and PDP-11 computers.
• When trying to create a FORTRAN compiler for the new system, Ken Thompson created the B language.

Why Was C Language Standardized?

• C was standardized by the American National Standards Institute (ANSI) in 1983, and by the International Organization for Standardization (ISO) in 1990.
• The standardization of C ensured compatibility and portability of C programs across different computer systems and hardware platforms.
• Prior to standardization, different versions of C existed with different syntax and libraries, making it difficult to port programs.

Defining Data

• Memory for data types (fundamental and derived) is defined in the following format:

  [data type] [variable name],...;
  

• Data is typically defined at the beginning of a function.
• C uses keywords like char, int, and float to define data types.
• Variables can be initialized with values during their declaration.

Data Types

Fundamental Data Types

• char: Stores a single character, takes up 1 byte of memory.
• int: Stores an integer value, typically takes up 4 bytes of memory.
• float: Stores a single-precision floating-point number, typically takes up 4 bytes of memory.

Derived Data Types

• Based on fundamental data types.
• short int: Stores an integer value, takes up 2 bytes of memory.
• long int: Stores an integer value, takes up 4 bytes of memory.
• double: Stores a double-precision floating-point number, typically takes up 8 bytes of memory.

C Character I/O

• Use the %c format specifier with scanf() to read a single character.
• Use the %c format specifier with printf() to display a character.
• ASCII values of characters can be displayed using the %d format specifier.

C Numeric I/O

• Use the %d format specifier with scanf() to read an integer.
• Use the %f format specifier with scanf() to read a single-precision floating-point number.
• Use the %lf format specifier with scanf() to read a double-precision floating-point number.

I/O Multiple Values

• Use multiple format specifiers within scanf() to read multiple values in a single line.

sizeof operator in C

• The sizeof operator returns the size of its operand in bytes at compile time.
• The result of sizeof is of the unsigned integral type size_t.
• You can use sizeof on various data types, including primitives, pointers, and compound types like structures and unions.

Operators in C

• Operators are special symbols used to perform operations on operands.
• Operators are classified based on the number of operands they take.

Unary Operators

• Applied to a single operand.
• Examples: increment (++), decrement (--), sizeof, type casting.

Binary Operators

• Applied to two operands.
• Examples: Arithmetic Operators, Relational Operators, Shift Operators, Logical Operators, Bitwise Operators, Conditional Operators, Assignment Operator, Misc Operator.

C Arithmetic Operators

• Perform mathematical operations on numerical values.

C Assignment Operators

• Used to assign a value to a variable.
• The most common assignment operator is =.

C Relational Operators

• Used in decision-making and loops.

C Bitwise Operators

• Used to perform operations on individual bits of data.
• Examples: AND (&), OR (|), XOR (^), NOT (~), Left Shift (<<), Right Shift (>>).
• Shift operators move bits to the left or right.
• Left shift (<<) multiplies the value by 2 for each position shifted.
• Right shift (>>) divides the value by 2 for each position shifted.

Loop Constructs

• C loops allow the execution of a sequence of statements multiple times.
• A loop consists of a body and a control statement.
• The control statement checks conditions for the loop's execution.
• Loops in C are used to repeat code execution.

Explore the fascinating evolution of the C programming language and the UNIX operating system. Discover how C was developed from predecessors like ALGOL and BCPL, and the key figures involved in its standardization. This quiz covers the timeline of significant events in the history of these two foundational technologies.