Introduction to C
C
Introduction – C was an offspring of the “BASIC COMBINED
PROGRAMMING LANGUAGE (BCPL) "called B, developed in 1960’s at the Cambridge
University.
B language was modified
by Dennis Ritchie and implemented at Bell laboratories in 1972. The new
language was named C. Since it was developed along with the UNIX operating
system, it is strongly associated with UNIX. UNIX was also developed at Bell
laboratories and was almost entirely coded in C.
C is general purpose
structured programming language and it combines the features of High Level
programming language with the elements of assemblers. Thus, it is close to both
man and machine, in this context, C is considered a middle level programming
language.
Structured
Programming -Structured
programming (sometimes known as modular programming) follows a top-down
approach, in which programmer separates the overall program structure into
different subsections.
Advantages
of Structured Programming
Reduced
Complexity
Easy
to Code
Take
less time
Easy
to debug
Reuse
of modules
Flow of control is clear
Features
of C Language
Structured
Middle
Level Language
Case
Sensitive
Extendable
Types of C language :
There are two different
types of C languages:
a.
Common C
b.
American National
Standard Institute (ANSI) C
Characteristics of C:
a. C can be used to develop both system and application
programs.
b. It has enough numbers of
in-built functions and operators and a variety of data types to represent
different kinds of data.
Advantages of C language :
a.
Program of C are easy to
read and maintain
b.
Programs are easy to
port across different computer platforms.
Data types supported by
C:
All C compilers support
four basic data types
a.
Integer (int)
b.
Character (char)
c.
Floating point (float)
d.
Double precision
floating point (double)
*note* Except the basic data types there are
many derived data type
Examples of
Derived Data Types – Arrays, Pointers, Structure, Unions, Enums, (Enum erations)
i)
Integer (int)- An Integer is a whole number either
positive, negative or zero but no decimal values. For example, 0, -5, 10
Declaring an
integer variable
int a,b
In the above example, the int keyword is used
to declare a and b as integer variables
ii)
float -It accepts Floating point values.
Declaring float
type variable
float b; b =
1.732
iii)
double- It also accepts the real numbers like
float data type but its range is higher than float data type
Declaring double
type variable
double x;
x = 67823.34456;
iv)
char- It holds only one character at a time.
Declaring char
type variable
char m;
v)
void – void data type has no value. Void
does not return a value.
Variable in C language: In C language you need to declare variables
explicitly. Declaration of a variable specifies its data type and name.
int x = 5; ( here int is data type, x is
variable name and 5 is the value)
float pi=3.14; (here float is data type, pi is
variable name and 3.14 is the value)
char grade = “t” ; ( here char is data type,
grade is variable name and t is text value.
A variable name can be up-to 31 characters long.
Constant – Constant is a value that cannot change during program
execution. The types of constant c supports are
Integer constant
Real constant
Character constant
String constant
C Token - C tokens are
the basic buildings blocks in C language which are constructed together to
write a C program. Each and every smallest individual unit in a C program are
known as C tokens. C tokens are of six types.
They are:
a) Keywords (eg:
int, while),
b) Identifiers
(eg: main, total)
c) Constants
(eg: 10, 20),
d) Strings (eg: “total”, “hello”)
e) Special
symbols (eg: (), {}),
f) Operators
(eg: +, /,-,*)
C keywords
(reserved word)-
Keyword is a set of special words which are already defined for some tasks. C
has only a set of 32 keywords, which have their predefined meaning and
cannot be used as a variable name. These words are also known as “reserved
words”.
Example of keywords – auto, int, char, void,
short, long, unsigned etc.
Identifiers -Identifiers
are the names given to the entities such as variables, functions, arrays
structures and unions.
For example
int price;
float total;
Here, price and
total are called identifiers
Rules for naming
Identifiers:
i)
The
Identifier must start with an alphabet or an under score (_).
ii)
Identifier
can be made from the combination of alphabets, digits and under score.
iii)
Not
any C keyword can be used as an Identifier.
iv)
Identifier
must be unique and can be used for a single purpose only.
C character set:
A character set denotes any alphabet, digit or
special symbol used to represent information. The C character set consist of
alphabets, upper case and lower case, the digits 0 – 9 and certain special
symbols ( + , -, {, }, & ). These are valid characters and can be used as
building blocks to construct basic program elements.
Format
Specifier-
The format specifier is used during input and output operation. It tells the
compiler what type of data is stored in
a variable during the input and output operation such as taking data from
keyboard and display data on the screen. Some examples are
|
Variable
or Data Type |
Format
Identifier |
|
Char |
%c |
|
Int |
%d |
|
long int |
%ld |
|
Float |
%f |
Operators used in C
language:
The operators used in C
language are:
i.
Arithmetic operator (+,
-, *, /, %) (a-b)
ii. Relational operator (=
=, < , >, <=, >=, !=) ( x<y)
iii. Logical operator (&&(AND), ( || (OR), ( ! (NOT) (
a&&b) (a||b) (!a)
iv. Assignment operator ( =,
+=, -=, *=, /=, %=)
v.
Unary operator
vi. Conditional operator. (
a>b ?a:b)
Header files – While writing program in C, we need to
include different header files in the beginning. Different library functions
are used to do different tasks in C language. For example, we use scanf()
function to ask data from keyboard. Each function is defined in a special type
of file. These files are called Header File and have extension .h. These header
files must be included using #include directive otherwise the compiler doesn’t
understand the library function we use and gives an error message. Examples of some header files – stdio.h,
string.h, math.h, ctype.h etc.
Library files- the
functions which are declared on header files such as stdio.h are known as
library files.
Here is the list of
some commonly used Header file and their purposes:
|
Header Files |
Purpose |
Functions Declared |
|
stdio.h |
Used for standard input and output
(I/O) operations. |
printf(), scanf(), getchar(),
putchar(), gets(), puts(), getc(), putc(), fopen, fclose(), feof() |
|
conio.h |
Contains declaration for console I/O
functions. |
clrscr(), exit() |
|
ctype.h |
Used for character-handling or testing
characters. |
isupper(), is lower, isalpha() |
|
math.h |
Declares mathematical functions and
macros. |
pow(), squr(), cos(), tan(), sin(),
log() |
|
stdlib.h |
Used for number conversions, storage
allocations. |
rand(), srand() |
|
string.h |
Used for manipulating strings. |
strlen(), strcpy(), strcmp(), strcat(),
strlwr(), strupr(), strrev() |
C program structure
A C program basically consists of
·
Preprocessor commands
·
Functions
·
Variables
·
Statements and expressions
·
Comments.
Rules to develop C program
·
C statements are entered in lower
case.
·
Every C statement ends with a
semicolon (;)
·
#
include is a directive/preprocessor statement and must be used at the beginning
of the program
·
C
program must start with main () function. This is the entry point of the
program
· In C language, each function is defined inside parenthesis { }
Source file
-------------> object file --------------------->executable file
C
compile .obj linker .exe
C is entirely functional
language and the primary function should be named as main ()
C program structure
#
include <header file>
main
()
{
Set
of statements
----------------------------
;
---------------------------
;
--------------------------
;
}
Example 1.
# include <stdio.h> /*creates programming environment by including the needed header files)*/
main () /*(begins execution of the program)*/
{
/*(denotes
the beginning of set of functions)*/
printf
(“hello world”) ;
}
The output of the
program – hello world
Explanation of the
program:
# include – (# include
is the first word of any C program, it is also known as pre-processor or
directive. The function of pre processor is to initialize the environment of
program, i.e. to link the program with the header file.
Header file
<stdio.h>- header file is a collection of library or built in functions
that helps us code in C. Header files contain definitions of functions and
variables which can be incorporated into any C program by pre processor #
include statement.
main ()- main () is a function that must be used in every C program, main function begins the execution of the program
printf () - it is a standard
library function to display data on screen.
scanf () – It allows to accept input from the keyboard.
*note* -
Each C statement must
be terminated by a semicolon(;).
/* comments */ - used
to write comments similar to REM in Qbasic.
Example 2.
#
include <stdio.h>
main
()
{
printf
(“hello world\n”) ; /* for new
line \n */
printf
(“good morning\”) ;
}
The
output of the program – hello world
good morning
example 3.
/*program
to find sum of two values */
#
include <stdio.h>
main
()
{
int
x;
int
y;
int
z;
x=5;
y=6;
z=x+y;
printf
(“\n the result is %d”,z);
}
example
4
/* program to find the sum of two
numbers accepting input from the user */
#include <conio.h>
void main()
{
clrscr()
int a,b,c;
printf ("Enter the first number
");
scanf("%d",&a);
printf ("Enter the second number
");
scanf("%d",&b);
c=a+b;
printf("Sum = %d",c);
getch();
}
*note*-The above C program asks any two
numbers from the keyboard and displays their sum. In this program, three
variables a,b and c are used and their types are declared as integer (int).
Unlike QBASIC, we need to declare the type and name of the variables in the
beginning of the program
Example 5
/* To find the product of any two
numbers */
#include <conio.h>
void main()
{
int a,b,c;
printf ("Enter the first number
");
scanf("%d",&a);
printf ("Enter the second number
");
scanf("%d",&b);
c=a*b;
printf("product = %d",c);
getch();
}
Example 6.
/* to accept character */
#include <stdio.h>
#include <conio.h>
void main()
{
char ch;
clrscr();
ch=getch();
printf("The typed character is
%c.",ch);
getch();
}
Example
7
/*program
to accept string */
#include
<stdio.h>
#include
<conio.h>
void main()
{
char name [20] ;
char add [30] ;
printf ("enter your name ");
scanf ("%s",name);
printf ("%s",name);
printf (“enter address”);
scanf ("%s”, add);
printf ("%s",add);
getch();
}
Example 8 of Arithmetic Calculation
/*
Calculate area and volume of a room*/
#include <stdio.h>
#include <conio.h>
void main()
{
clrscr();
int l,b,h,a,v;
printf ("Type length, breadth and
height ");
scanf
("%d%d%d",&l,&b,&h);
a=l*b;
v=l*b*h;
printf("\nArea=%d",a);
printf ("\nVolume=%d",v);
getch();
}
Example 9 of Arithmetic Calculation
/* Calculate total marks and percentage
*/
#include <stdio.h>
#include <conio.h>
void main()
{
clrscr();
int e,m,c,t;
float p;
printf("Marks in English, Math
& Computer ");
scanf("%d%d%d",&e,&m,&c);
t=e+m+c; p=t/3; //Full mark for all
subject is 100
printf("\nTotal Marks = %d
",t); printf("\nPercentage = %f ",p);
getch();
}
Control structures in C
C supports three types of basic control
structures, which are used to alter the flow of execution of the program.
a) Sequence structure (straight line
paths)
b) Selection structure (one or many
branches)
c) Loop structure (repetition of a set
of activities)
a) Sequential Structure- In
sequential structure, the statements are executed one after another
sequentially from top to bottom without changing the flow of program.
b) Selection Structure- It is
also called branching structure. In this structure, the control of the program
is transferred from one part of the program to another on the basis of
specified condition or without condition.
c) Looping Structure- Looping is
the process of repeating the execution of a statement or a block of statements
guided by a condition. A loop is terminated when the given condition is
satisfied.
if statement- if statement
is used to test one or more condition and execute statement(s) if the given
condition is True.
Syntax: if (condition)
{
statements …………………
}
If the condition mentioned in the syntax
is True, then the statements written inside the parenthesis { } will be
executed.
Example of if statement
#include <stdio.h>
#include <conio.h>
void main()
{
int a;
printf ("Type your marks ");
scanf ("%d",&a);
if(a>=40)
{
printf ("You are Pass");
printf
("\nCongratulations!!!");
}
getch();
}
if … else statement-This statement
is used to check one or more condition and execute the condition either the
condition is True or False.
Syntax : if (condition)
{
statements …………..
}
Else
{
statements …………..
}
Example of if ....else statement
#include <stdio.h>
#include <conio.h>
void main()
{
int a;
clrscr();
printf ("Type your marks ");
scanf ("%d",&a);
if(a>=40)
{
printf ("You are Pass");
}
Else
{
printf ("You are Fail");
}
getch();
}
Example of Logical Calculation #1
/*Check ODD or EVEN*/
#include <stdio.h>
#include <stdio.h>
void main()
{
clrscr();
int n;
printf("Type any number ");
scanf("%d",&n);
if (n%2==0)
printf ("\nIt is even.");
}
else
{
printf ("\nIt is odd.");
}
getch();
}
Example of Logical Calculation #2
/* Find the GREATER number */
#include <stdio.h>
#include <conio.h>
int main()
{
clrscr();
int a,b;
printf("Type first number ");
scanf("%d",&a);
printf("Type second number ");
scanf("%d",&b);
if(a>b)
{
printf("Greater number is %d
",a);
}
else
{
printf("Greater number is %d
",b);
} getch();
return 0;
}
Looping in C
The looping statement allows a set of instructions
to be performed repeatedly until a certain condition is fulfilled. The looping
statements are also called iteration statements.
Looping statements in C
C provides three kinds of loops:
i)
while
loop
ii)
do
loop
iii)
for
loop
i)
while loop -The while loop continues executing a
block of code till the given condition is t rue. The loop will be terminated
when the condition becomes false.
Example:
of while loop
#include
<stdio.h>
#include
<conio.h>
void
main()
{
int
num=1;
clrscr();
while
(num<=10);
{
printf
("%d ",num);
num++;
}
getch();
}
ii)
do loop - The do loop also executes a block of
code as long as a condition is satisfied. The difference between a
"do" loop and a "while" loop is that the while loop tests
its condition before the execution of loop; the "do" loop tests its
condition after the execution of loop.
Example
of do loop
#include
<stdio.h>
#include
<conio.h>
void
main()
{
int
num=1;
clrscr();
do
{
printf
("%d ",num);
num++;
}
while
(num<=10);
getch();
}
for
loop-
The for loop can execute a block of code for a fixed number of repetitions. It
is easy to use and defined in a single statement.
Example
of for loop
#include
<stdio.h>
#include
<conio.h>
void
main()
{
clrscr();
int
c;
for
(c=1;c<=10;c++)
{
printf
("%d ",c);
}
getch();
}
Program
to generate Fibonacci series
//Fibonocci
series 1 2 3 5 8 13 ...
#include
<stdio.h>
#include
<conio.h>
void
main()
{
clrscr();
int a=1,b=2,c,n=1;
do
{
printf
("%d ",a);
c=a+b;
a=b; b=c;
n++;
}
while
(n<=10);
getch();
}
//program
to Check PRIME or COMPOSITE
#include
<stdio.h>
#include
<conio.h>
void
main()
{
clrscr();
int n,i,c=0;
printf
("Type any number ");
scanf
("%d",&n);
for
(i=2;i<=n-1;i++)
{
if(n%i==0) c++;
}
if
(c==0)
printf("The
number is prime. ");
else
printf("The
number is composite. ");
getch();
}
Similarity between C and
Qbasic:
i.
Both language can be
used to develop structured programs.
ii.
Both languages support
local and global variables as well as procedures.
Differences between C
and Qbasic
i. Qbasic is a high level
language whereas C is considered a middle level language.
ii. Qbasic is used for
developing elementary application programs whereas C can be used to develop
both system and application software.
iii. C has 32 keywords
whereas qbasic uses 163 or more keywords.
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