Short Notes: Introduction to C, Structure of C Programming | Short Notes for Computer Science Engineering - Computer Science Engineering (CSE) PDF Download

 Page 1


INTRODUCTION TO C
Brief History of C
> The C programming language is a structure oriented programming language, developed at 
Bell Laboratories in 1972 by Dennis Ritchie.
> C programming language features were derived from an earlier language called “B”
(Basic Combined Programming Language - BCPL)
> C language was invented for implementing UNIX operating system.
> In 1978, Dennis Ritchie and Brian Kernighan published the first edition “The C 
Programming Language” and is commonly 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.
> Many of C’s ideas & principles were derived from the earlier language B, thereby naming 
this new language “C”.
• Algol
• BCPL
• B
• T rad itio n al C
• K & RC
• A N S I C
• A N S I / ISO C
* C 99
Taxonomy of C Language
Page 2


INTRODUCTION TO C
Brief History of C
> The C programming language is a structure oriented programming language, developed at 
Bell Laboratories in 1972 by Dennis Ritchie.
> C programming language features were derived from an earlier language called “B”
(Basic Combined Programming Language - BCPL)
> C language was invented for implementing UNIX operating system.
> In 1978, Dennis Ritchie and Brian Kernighan published the first edition “The C 
Programming Language” and is commonly 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.
> Many of C’s ideas & principles were derived from the earlier language B, thereby naming 
this new language “C”.
• Algol
• BCPL
• B
• T rad itio n al C
• K & RC
• A N S I C
• A N S I / ISO C
* C 99
Taxonomy of C Language
WHY IS C POPULAR
> It is reliable, simple and easy to use.
> C is a small, block-structured programming language.
> C is a portable language, which means that C programs written on one system can be run 
on other systems with little or no modification.
> C has one of the largest assortments of operators, such as those used for calculations and 
data comparisons.
> Although the programmer has more freedom with data storage, the languages do not 
check data type accuracy for the programmer.
WHY TO STUDY C
> By the early 1980s, C was already a dominant language in the minicomputer world of 
Unix systems. Since then, it has spread to personal computers (microcomputers) and to 
mainframes.
> Many software houses use C as the preferred language for producing word processing 
programs, spreadsheets, compilers, and other products.
> C is an extremely flexible language—particularly if it is to be used to write operating 
systems.
> Unlike most other languages that have only four or five levels of precedence, C has 15.
CHARECTERESTICS OF A C PROGRAM
> Middle level language.
High Level Middle Level Low Level
High level languages 
provide 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
Examples: 
Java, Python
C, C++ Assembler
> Small size - has only 32 keywords
> Extensive use of function calls- enables the end user to add their own functions to the C 
library.
> Supports loose typing - a character can be treated as an integer & vice versa.
> Structured language
Page 3


INTRODUCTION TO C
Brief History of C
> The C programming language is a structure oriented programming language, developed at 
Bell Laboratories in 1972 by Dennis Ritchie.
> C programming language features were derived from an earlier language called “B”
(Basic Combined Programming Language - BCPL)
> C language was invented for implementing UNIX operating system.
> In 1978, Dennis Ritchie and Brian Kernighan published the first edition “The C 
Programming Language” and is commonly 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.
> Many of C’s ideas & principles were derived from the earlier language B, thereby naming 
this new language “C”.
• Algol
• BCPL
• B
• T rad itio n al C
• K & RC
• A N S I C
• A N S I / ISO C
* C 99
Taxonomy of C Language
WHY IS C POPULAR
> It is reliable, simple and easy to use.
> C is a small, block-structured programming language.
> C is a portable language, which means that C programs written on one system can be run 
on other systems with little or no modification.
> C has one of the largest assortments of operators, such as those used for calculations and 
data comparisons.
> Although the programmer has more freedom with data storage, the languages do not 
check data type accuracy for the programmer.
WHY TO STUDY C
> By the early 1980s, C was already a dominant language in the minicomputer world of 
Unix systems. Since then, it has spread to personal computers (microcomputers) and to 
mainframes.
> Many software houses use C as the preferred language for producing word processing 
programs, spreadsheets, compilers, and other products.
> C is an extremely flexible language—particularly if it is to be used to write operating 
systems.
> Unlike most other languages that have only four or five levels of precedence, C has 15.
CHARECTERESTICS OF A C PROGRAM
> Middle level language.
High Level Middle Level Low Level
High level languages 
provide 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
Examples: 
Java, Python
C, C++ Assembler
> Small size - has only 32 keywords
> Extensive use of function calls- enables the end user to add their own functions to the C 
library.
> Supports loose typing - a character can be treated as an integer & vice versa.
> Structured language
Structure oriented Object oriented Non structure
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
Prime focus is on functions and 
procedures that operate on the 
data
Prime focus is in the data that is 
being operated and not on the 
functions or procedures
N/A
Data moves freely around the 
systems from one function to 
another
Data is hidden and cannot be 
accessed by external functions
N/A
Program structure follows “Top 
Down Approach”
Program structure follows 
“Bottom UP Approach”
N/A
Examples:
C, Pascal, ALGOL and Modula-2
C++, JAVA and C# (C sharp) BASIC, COBOL, 
FORTRAN
> Low level (Bit Wise) programming readily available
> Pointer implementation - extensive use of pointers for memory, array, structures and 
functions.
> It has high-level constructs.
> It can handle low-level activities.
> It produces efficient programs.
> It can be compiled on a variety of computers.
USES
The C programming language is used for developing system applications that forms a major 
portion of operating systems such as Windows, UNIX and Linux. Below are some examples of C 
being used:
> Database systems
> Graphics packages
> Word processors
> Spreadsheets
> Operating system development
> Compilers and Assemblers
> Network drivers
> Interpreters
Page 4


INTRODUCTION TO C
Brief History of C
> The C programming language is a structure oriented programming language, developed at 
Bell Laboratories in 1972 by Dennis Ritchie.
> C programming language features were derived from an earlier language called “B”
(Basic Combined Programming Language - BCPL)
> C language was invented for implementing UNIX operating system.
> In 1978, Dennis Ritchie and Brian Kernighan published the first edition “The C 
Programming Language” and is commonly 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.
> Many of C’s ideas & principles were derived from the earlier language B, thereby naming 
this new language “C”.
• Algol
• BCPL
• B
• T rad itio n al C
• K & RC
• A N S I C
• A N S I / ISO C
* C 99
Taxonomy of C Language
WHY IS C POPULAR
> It is reliable, simple and easy to use.
> C is a small, block-structured programming language.
> C is a portable language, which means that C programs written on one system can be run 
on other systems with little or no modification.
> C has one of the largest assortments of operators, such as those used for calculations and 
data comparisons.
> Although the programmer has more freedom with data storage, the languages do not 
check data type accuracy for the programmer.
WHY TO STUDY C
> By the early 1980s, C was already a dominant language in the minicomputer world of 
Unix systems. Since then, it has spread to personal computers (microcomputers) and to 
mainframes.
> Many software houses use C as the preferred language for producing word processing 
programs, spreadsheets, compilers, and other products.
> C is an extremely flexible language—particularly if it is to be used to write operating 
systems.
> Unlike most other languages that have only four or five levels of precedence, C has 15.
CHARECTERESTICS OF A C PROGRAM
> Middle level language.
High Level Middle Level Low Level
High level languages 
provide 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
Examples: 
Java, Python
C, C++ Assembler
> Small size - has only 32 keywords
> Extensive use of function calls- enables the end user to add their own functions to the C 
library.
> Supports loose typing - a character can be treated as an integer & vice versa.
> Structured language
Structure oriented Object oriented Non structure
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
Prime focus is on functions and 
procedures that operate on the 
data
Prime focus is in the data that is 
being operated and not on the 
functions or procedures
N/A
Data moves freely around the 
systems from one function to 
another
Data is hidden and cannot be 
accessed by external functions
N/A
Program structure follows “Top 
Down Approach”
Program structure follows 
“Bottom UP Approach”
N/A
Examples:
C, Pascal, ALGOL and Modula-2
C++, JAVA and C# (C sharp) BASIC, COBOL, 
FORTRAN
> Low level (Bit Wise) programming readily available
> Pointer implementation - extensive use of pointers for memory, array, structures and 
functions.
> It has high-level constructs.
> It can handle low-level activities.
> It produces efficient programs.
> It can be compiled on a variety of computers.
USES
The C programming language is used for developing system applications that forms a major 
portion of operating systems such as Windows, UNIX and Linux. Below are some examples of C 
being used:
> Database systems
> Graphics packages
> Word processors
> Spreadsheets
> Operating system development
> Compilers and Assemblers
> Network drivers
> Interpreters
STRUCTURE OF A C PROGRAM
The structure of a C program is a protocol (rules) to the programmer, which he has to follow 
while writing a C program. The general basic structure of C program is shown in the figure 
below.
( Documentations )
(P re process or statements)
C Global dedarations ")
Main ( )
{
Local declarations 
Program statements
Calling user defined functions (option to user)
}
User defined functions 
Function 1 
Function 2 
Function n
Body of the 
Main ( ) function
(Option to user)
Based on this structure, we can sketch a C program.
Example:
/* This program accepts a number & displays it to the user*/
#include <stdio.h> 
void main(void)
{ int number;
printf( "Please enter a number: " ); 
scanf( "%d", &number ); 
printf( "You entered %d", number); 
return 0;}
Page 5


INTRODUCTION TO C
Brief History of C
> The C programming language is a structure oriented programming language, developed at 
Bell Laboratories in 1972 by Dennis Ritchie.
> C programming language features were derived from an earlier language called “B”
(Basic Combined Programming Language - BCPL)
> C language was invented for implementing UNIX operating system.
> In 1978, Dennis Ritchie and Brian Kernighan published the first edition “The C 
Programming Language” and is commonly 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.
> Many of C’s ideas & principles were derived from the earlier language B, thereby naming 
this new language “C”.
• Algol
• BCPL
• B
• T rad itio n al C
• K & RC
• A N S I C
• A N S I / ISO C
* C 99
Taxonomy of C Language
WHY IS C POPULAR
> It is reliable, simple and easy to use.
> C is a small, block-structured programming language.
> C is a portable language, which means that C programs written on one system can be run 
on other systems with little or no modification.
> C has one of the largest assortments of operators, such as those used for calculations and 
data comparisons.
> Although the programmer has more freedom with data storage, the languages do not 
check data type accuracy for the programmer.
WHY TO STUDY C
> By the early 1980s, C was already a dominant language in the minicomputer world of 
Unix systems. Since then, it has spread to personal computers (microcomputers) and to 
mainframes.
> Many software houses use C as the preferred language for producing word processing 
programs, spreadsheets, compilers, and other products.
> C is an extremely flexible language—particularly if it is to be used to write operating 
systems.
> Unlike most other languages that have only four or five levels of precedence, C has 15.
CHARECTERESTICS OF A C PROGRAM
> Middle level language.
High Level Middle Level Low Level
High level languages 
provide 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
Examples: 
Java, Python
C, C++ Assembler
> Small size - has only 32 keywords
> Extensive use of function calls- enables the end user to add their own functions to the C 
library.
> Supports loose typing - a character can be treated as an integer & vice versa.
> Structured language
Structure oriented Object oriented Non structure
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
Prime focus is on functions and 
procedures that operate on the 
data
Prime focus is in the data that is 
being operated and not on the 
functions or procedures
N/A
Data moves freely around the 
systems from one function to 
another
Data is hidden and cannot be 
accessed by external functions
N/A
Program structure follows “Top 
Down Approach”
Program structure follows 
“Bottom UP Approach”
N/A
Examples:
C, Pascal, ALGOL and Modula-2
C++, JAVA and C# (C sharp) BASIC, COBOL, 
FORTRAN
> Low level (Bit Wise) programming readily available
> Pointer implementation - extensive use of pointers for memory, array, structures and 
functions.
> It has high-level constructs.
> It can handle low-level activities.
> It produces efficient programs.
> It can be compiled on a variety of computers.
USES
The C programming language is used for developing system applications that forms a major 
portion of operating systems such as Windows, UNIX and Linux. Below are some examples of C 
being used:
> Database systems
> Graphics packages
> Word processors
> Spreadsheets
> Operating system development
> Compilers and Assemblers
> Network drivers
> Interpreters
STRUCTURE OF A C PROGRAM
The structure of a C program is a protocol (rules) to the programmer, which he has to follow 
while writing a C program. The general basic structure of C program is shown in the figure 
below.
( Documentations )
(P re process or statements)
C Global dedarations ")
Main ( )
{
Local declarations 
Program statements
Calling user defined functions (option to user)
}
User defined functions 
Function 1 
Function 2 
Function n
Body of the 
Main ( ) function
(Option to user)
Based on this structure, we can sketch a C program.
Example:
/* This program accepts a number & displays it to the user*/
#include <stdio.h> 
void main(void)
{ int number;
printf( "Please enter a number: " ); 
scanf( "%d", &number ); 
printf( "You entered %d", number); 
return 0;}
Stepwise explanation: 
#include
> The part of the compiler which actually gets your program from the source file is called 
the preprocessor.
¦ #include <stdio.h>
> #include is a pre-processor directive. It is not really part of our program, but instead it is 
an instruction to the compiler to make it do something. It tells the C compiler to include 
the contents of a file (in this case the system file called stdio.h).
> The compiler knows it is a system file, and therefore must be looked for in a special place, 
by the fact that the filename is enclosed in <> characters
<stdio.h>
> stdio.h is the name of the standard library definition file for all STanDard Input and 
Output functions.
> Your program will almost certainly want to send information to the screen and read things 
from the keyboard, and stdio.h is the name of the file in which the functions that we want 
to use are defined.
> The function we want to use is called printf. The actual code of printf will be tied in later 
by the linker.
> The ".h" portion of the filename is the language extension, which denotes an include file.
void
> This literally means that this means nothing. In this case, it is referring to the function 
whose name follows.
> Void tells to C compiler that a given entity has no meaning, and produces no error.
main
> In this particular example, the only function in the program is called main.
> A C program is typically made up of large number of functions. Each of these is given a 
name by the programmer and they refer to each other as the program runs.
> C regards the name main as a special case and will run this function first i.e. the program 
execution starts from main.
(void)
> This is a pair of brackets enclosing the keyword void.
> It tells the compiler that the function main has no parameters.
> A parameter to a function gives the function something to work on.