Language History

C – Language History

• C language is a structure oriented programming language, was developed at Bell Laboratories in 1972 by Dennis Ritchie
• C features were derived from earlier language called “B” (BCPL language)
• C was invented for implementing UNIX operating system
• In 1978, Dennis Ritchie and Brian Kernighan published the first edition  “The C Programming Language” and commanly known as K&R C
• In 1983, the American National Standards Institute (ANSI) established a committee to provide a modern, comprehensive definition of C. The resulting definition, the ANSI standard, or “ANSI C”, was completed late 1988.

C standards

• C89/C90 standard – First standardized specification for C language was developed by American National Standards Institute in 1989. C89 and C90 standards refer to the same programming language.
• C99 standard – Next revision was published in 1999 that introduced new futures like advanced data types and other changes.

C11 and Embedded C

• C11 standard adds new features to C and library like type generic macros, anonymous structures, improved Unicode support, atomic operations, multi-threading, and bounds-checked functions. It also makes some portions of the existing C99 library optional, and improves compatibility with C++.
• Embedded C includes features not available in normal C like fixed-point arithmetic, named address spaces, and basic I/O hardware addressing
• Operating systems, C compiler, all UNIX application programs are written in C

• It is also called as procedure oriented programming language
• C language is reliable, simple and easy to use.
• C has been coded in assembly language

Features of C language:

• Reliability
• Portability
• Flexibility
• Interactivity
• Modularity
• Efficiency and Effectiveness

Uses of C language:

     C is used for developing system applications that forms portion of operating system. Below are some examples of C being used.

• Database systems
• Graphics packages
• Word processors
• Spread sheets
• Operating system development
• Compilers and Assemblers
• Network drivers
• Interpreters
  

  Which level the C language belonging to?

  S.no	High Level	Middle Level	Low Level
  1	High level languages provides almost everything that the programmer might need to do as already built into the language	Middle level languages don’t provide all the built-in functions found in high level languages, but provides all building blocks that we need to produce the result we want	Low level languages provides nothing other than access to the machines basic instruction set
  2	Examples:Ada, BASIC, COBOL, FORTRAN, Modula-2	C, C++, JAVA, FORTH, Macro-Assembler	Assembler

  C is a structured language

  S.no	Structure oriented	Object oriented	Non structure
  1	In this type of language, large programs are divided into small programs called functions	In this type of language, programs are divided into objects	There is no specific structure for programming this language
  2	Prime focus is on functions and procedures that operate on data	Prime focus is on the data that is being operated and not the functions or procedures	N/A
  3	Data moves freely around the systems from one function to another	Data is hidden and cannot be accessed by external functions	N/A
  4	Program structure follows “Top Down Approach”	Program structure follows “Bottom UP Approach”	N/A
  5	Examples: BASIC, COBOL, FORTRAN	C, C++, JAVA, Ada, Pascal, Modula-2	Assembler

  Key points to remember:

• C is structured, middle level programming language developed by Dennis Ritchie
• Operating system programs such as Windows, Unix, Linux are wriiten by C language
• C89/C90 and C99 are two standardized editions of C
• C has been written in assembly language  

Data Type in 'C'

Father of C                                         - Dennis Ritchie

First Computer Programmer             - Ada

Cut                                                      - shift + del

Paste                                                   - shift + insert

Copy                                                    - ctrl + insert

Clear                                                   - ctrl + del

Compile                                              - alt + F9

Run                                                     - ctrl + F9

To see the output                                - alt + F5        

1.       Data Type in C

Data Type                              Meaning                                             Size (in bytes)

char(Range -128 to +127)       a character                                           1

int(Range -32768 to +32767) an integer                                              2

float                                         a single precision real number               4

double                                     a double precision real number             8

void                                         valueless                                              0

(The void data type is not  used as often as the above four.)

                                                C Data Types

                                                     |

                        |--------------------------------------------|

            Primary Data Types             Secondary Data Types

            1. Character                                         1. Array

              i. Unsigned Char

              ii. Signed Char

            2. Integer                                             2. Pointer

              i. Short

              ii. Long

            3. Float                                                3. Structure

            4. Double                                            4. Union

            5. Void                                                5. Enum etc.

Integers

- Integers data type can be categorised into two parts;Long and short.

- Long integers require twice the space in memory than ordinary integers do.

- Therefore long integers occupy four bytes of memory.

- The value of a long integer can vary form -2147483648 to +2147483647.

- Long integers declared using the keywords long. For example:

            long int i;

- Short integers require less space in memory and thus speed up the program execution.

- Short integer is nothing but our ordinary int.

- Short integers are declared using keywords int. For example:

            int i;

- If we add the suffix 'L' or 'l' at the end of the number, then it would be becoming as a long integer and hence occupy 4 bytes.

Constants and Variables

- A constant is a quantity that does not change. This quantity can be stored at a location in the memory of the computer.

- Real constants are often called Floating Point constants.

- The real constants could be written in two forms; Fractional (426.0, +325.34,-32.76) and Exponential (+3.2e-5, 4.1e8,-3.2e-5) Form.

- Range of real constant expressed in exponential form is -3.4e38 to 3.4e38.

- The part appearing before 'e' is called mantissa, whereas the part following 'e' is called exponential.

- In place of a small case 'e' a capital 'E' can also be used.

Rules for Constructing Variable Names

- A variable name is any combination of 1 to 8 alphabets, digits or underscores.

- Some compilers allow variables names whose length could be upto 40 characters. But it is recommended to stick on 8 characters.

- The first character in the variable name must be an alphabet.

- No commas, blanks or special character (except underscore) are allowed within a variable name.

Scope of Variables

- Variables can have two types of scopes: Local and Global.

- A variable with a global scope is accessible to all the statements in the program, whereas the one with local scope is available only to certain selected statements in the program.

- Global variables are declared outside all functions whereas the local variables are defined inside a function.

C Keywords

- Keywords also known as 'Reserved Word'.

- Keywords are the words whose meaning has already been explained to the C compiler.

- The keywords cannot be used as variable names.

- There are 32 keywords available in C, for example: break, case, else, char, if, for, void etc.

C Programming

- A comment can be enclosed within /*  */ (for multiple line comment) or // (for single line comment).

Printf(): It is a function which is used to print the value contained in a variable on the screen.

            Syntax: printf("<format string">,<list of variable>);

                        <format string> could be %c (for character), %d(for integer),%f(for float values).

            Example: printf("%d",n1);

/n: It is called a newline and takes the cursor to the next line.

            Example: printf("Average=%d\nSum=%d",avg,sum);

           

Scanf(): It is used for supplying the values in the variables.

            Syntax: scanf("<format string">,&<list of variable>);

            Example: scanf("%d",&n1);

Integers, Signed & Unsigned

When we know in advance that the stored value in a given integer variable will always be positive, then we can declare the variable to be unsigned, as in;

            unsigned int car_park;

With such a declaration, the range of permissible integer values will shift from the range -32768 to +32767 to the range 0 to 65535. Thus declaring the integers as unsigned almost doubles the size of the largest possible value. Unsigned integer occupies two bytes. The following unsigned declarations are same;

            short unsigned int i;

unsigned int i;

unsigned i;

The way there exists a short unsigned int, there also exists a long unsigned int which has a range of 0 to 4294967295 and occupies four bytes of memory.

By default a short int is a signed short int and a long int is a signed long int.

Char, Signed & Unsigned

Signed and unsigned chars, both occupying one byte each, but having different range.

A signed character is same as our ordinary char and has a range from -128 to +127; whereas an unsigned char has a range from 0 to 255.

#include<stdio.h>

void main

{

            char ch=291;

            printf(“%d%c\n”,ch,ch);

}

Output is

            35        #

Since variable ch has defined as char, therefore it cannot take a value bigger than +128. But when value exceeds +127, an appropriate value from the other side of the range is picked up and stored in ch. In this case, value is 35 and its corresponding character is # get printed.

Program1:

#include<stdio.h>

void main()

{

            char c;

            unsigned char d;

            int i;

            unsigned int j;

            long int k;

            unsigned long int m;

            float x;

            double y;

            scanf(“%c%c”,&c,&d);

            printf(“%c%c”,c,d);

            scanf(“%d%u”,&i,&j);

            printf(“%d%u”,i,j);

            scanf(“%ld%lu”,&k,&m);

            printf(“%ld%lu”,k,m);

            scanf(“%f%lf”,&x,&y);

            printf(“%f%lf”,x,y);

getch();

}