OpenGurukul : Language : C Programming

C Programming

By
OpenGurukul Team

www.opengurukul.com

C Programming

Introduction

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Introduction : History
1960 ALGOL In te rn a tion a l G rou p

1967 BCPL
Ma rtin R ic h a rd s

1970
B Ke n T h om p s on

1972 Traditional C D e n n is R itc h e


Introduction : Features
Extensive use of function calls
Structured language
Pointer implementation - extensive use of pointers for memory,
array, structures and functions.
C has now become a widely used professional language for
various reasons.
General purpose programming language.
Helps in development of both system as well as application
software.
C is a highly portable language.
This means it can be run on different machines .

Introduction : Program Structure
Documentation
Preprocessor directives / header files
Type definitions
Function prototypes -- declare function types and variables
passed to function.
The main() function
Other Functions


Introduction : C program : Example
Program : Compilation of C Program
$ cat hello.c $ gcc hello.c -o hello
#include <stdio.h> $

main() Execution of Program

{ $ ./hello
Hello World
printf("Hello Worldn");
$
}


Introduction : Input and output
The printf(“control string”, arg_list) is a function to print formatted
output.
Control string contains format specifier(%) and string of characters to
be printed.
Each % indicates the argument to be substituted in what form it has to
be printed. e.g. %d is used for integer argument.
e.g, printf(“the value of x is %d”,x);
The scanf(“control string”, &variable) is just like printf(). It reads input
instead of writing output.
e.g. scanf(“%d”, &x);
Note:
&-- address of operator.
We can also specify width while displaying data. e.g. %6d will print a
decimal integer at least 6 characters wide.
For floating point, to point 2 characters after decimal point, use %.2f

Introduction : I/O : Example
Program :
#include <stdio.h> OUTPUT :
Enter a number : 10
main()
number = 10
{
int x;
printf("Enter a number : ");
scanf("%d", &x);
printf("number = %dn", x);
return 0;
}

Comments
Single line comment can be specified using //
// single line comment

Multi line comment can be specified using /* */
/*
* Multi line comment 1
* Multi line comment 2
*/


C programming

Data Types
&
Variables


Identifiers
Identifiers are names given to the elements such as variables,
arrays and functions that are used in a program
Basically, these identifiers are sequence of alphabets and digits
There are certain rules that govern the formation of identifiers,
based on those rules the following are the VALID and INVALID
identifiers :
Valid identifiers:
Marks, TOTAL_MARKS , gross_salary_1998, Area_of_circle(), Num[20]

Invalid identifiers:
8ab, TOTAL MARK, Gross-salary-1997, Area_ _ of _ _ circle


Data Types & Sizes
Data types Qualifiers - unsigned & signed
char - single byte - can store one applies to char and integer
character
default may be signed or unsigned (it
int - integer - generally natural size depends on the platform).
float - for single precision floating
point
Range
double - for double precision floating
point unsigned char : 0, 255 (2^8-1)

Qualifiers - short & long signed char : -128 (-2^7), +127
(2^7-1)
short and long provides different
length of integers.
short int - 2 bytes
long int - 4 bytes (32-bit systems), 8
bytes(64-bit systems) www.opengurukul.com 12

Data Types & Sizes

Ty p e S iz e Rang e fo rm
char 1 b y te -1 2 8 to 127 %c ‘a ’ ‘A ’ ‘# ’ ‘n ’
u n s ig n e d 1 b y te 0 to 255
char
in t 2 b y te -3 2 7 6 8 to % d -2 5 5 0 -5
32767
u n s ig n e d in t 2 b y te 0 to 6 5 5 3 5 % u 25u 32768u
lon g in t 4 b y te -2 1 4 7 4 8 3 6 4 8 to % ld 4 5 l -5 l 40000l
+ 2147483647

u n s ig n e d 4 b y te 0 to % lu 1 0 0 lu 5 1 lu
lon g 4294967295
floa t 4 b y te ± 3 .4 * 1 0 ^ ± 3 8 %f -3 .5 f 7 .5 f
d ou b le 8 b y te ± 1 .7 * 1 0 ^ ± 3 0 8 % lf -3 .5 7 .5
lon g d ou b le 1 0 b y te ± 3 .4 * % L f -3 .5 L 7 .5 L
10^ ± 4932

Data types: Example
#include <stdio.h> Output:
int main(void) { sizeof char = 1
printf("sizeof char = %dn", sizeof(char)); sizeof short = 2
printf("sizeof short = %dn", sizeof(short)); sizeof int = 4
printf("sizeof int = %dn", sizeof(int));
sizeof long = 4
printf("sizeof long = %dn", sizeof(long));
sizeof float = 4
printf("sizeof float = %dn", sizeof(float));
sizeof double = 8
printf("sizeof double = %dn", sizeof(double));
return 0;
}


Variables
It is a data name that is used to store a data value.
Variables can take different values at different times during
execution.
All the variables must be declared before they are used.
Example:
Declaration:

int x; float y;

Initialization:

x=10; y=10.5;


Variable Names
There are certain conditions to be followed before the declaration of a
variable :
. They must begin with a letter
. Uppercase and lowercase are significant
. It should not be a keyword
. White space is not allowed
Examples of valid variable names:
John value x1 T_cut
Examples of Invalid variable names:
123 % 21th (area)
The underscore "_" counts as a letter. It is very useful for readability of
long variable names.
Don't begin your variable name with "_" as system library routines uses16
www.opengurukul.com
such names.

Variable Names
Names are made up of letters and digits.
First character must be letter.
The underscore "_" counts as a letter. It is very useful for readability of
long variable names.
Don't begin your variable name with "_" as system library routines uses
such names.
Traditional practice - use lower case for variable names, use upper case
for symbolic constants.
Keywords such as if, else, int are reserved. These cannot be used as
variable names.
Use shorter names for local variables. Use longer names for
global/external variables.

Variable Declarations
All variables must be declared before use. A declaration announces
property (data type) of the variable.
The declaration is usually done at the beginning of the block(function)
The declaration must be done before any executable statements in a
block (function).
A declaration specifies a type and contains a list of one or more
variables of that type, as in
int lower, upper, step;
A variable may also be initialized in its declaration. If the name is
followed by an equal signs and an expression, the expression serves
as an initializer, as in
int i = 0;

Constants
The term constant means that it does not change during the execution of
program
There are four basic types of constants in C
1.Integer constants
2.Floating-point constants
3.Character constants
4.String constants

Comma and blank spaces cannot be included within the constants.
Constants can be preceded by a – or + sign, if desired. If either sign does not
precede the constant it is assumed to be positive.
The value of a constant cannot exceed specified minimum and maximum
bounds. www.opengurukul.com 19

Constants : Integer : Example
#include <stdio.h> Output :
#include <stdlib.h> x = 10
int main() y = 255
{
int x = 012;
int y = 0xFF;
printf("x = %dn", x);
printf("y = %dn", y);
return 0;
}

Constant : Character : Example
#include<stdio.h> Output
int main() c=x
{
const char c = 'x';
printf(“c = %cn”, c);
return 0;
}


Constant : String : Example
#include<stdio.h> Output

Int main() s = Open Gurukul

{
const char *s = ”Open Gurukul”;
printf(“s = %sn”, s);
return 0;
}


C Programming

Operators


Operators
An operator is a symbol that tells the compiler to perform specific
operation.

Operator are classified into 3 types based upon no. of operands.

Unary operator: Required only one operand
Binary operator: Required only two operand
Ternary: Required only three operand


OPERATORS

Unary operator Binary operator Ternary operator

Pre Increment/ Decrement Arithmetic Operator Ternary Operator
Post Increment/ Decrement Logical Operator
Size Estimating Operator Relational Operator
Address of(&) Assignment Operator
Pointer operator(*) Conditional Operator
Special Operator Bit wise Operator


Priority
parenthesis ( )

u n a ry !, + , -, + + , -- (p re in c re m e n t/d e c re m e n t)

a rith m e tic *, /, %
Airthmetic
a rith m e tic +,-

re la tion a l <,>,<=,>=
Relational
re la tion a l = = , !=

log ic a l a n d &&
Logical
log ic a l or ||

c on d ition a l ?: Ternary

a s s ig n m e n t =

Pos t www.opengurukul.com 26
in c re m e n t/d e c + + , --
re m e n t

Operators : Arithmetic : Example
PROGRAM:
#include<stdio.h>
#include<stdlib.h>
main() {
int num1, num2, sum, sub, mul, div;
scanf("%d %d", &num1, &num2);
sum = num1 + num2; printf("nsum = %d, ", sum);
sub = num1 – num2; printf("diff = %d, ", sub);
mul = num1*num2; printf(" product = %d, ", mul);
div = num1 / num2; printf("division = %dn", div);
}
OUTPUT : 4 5
sum = 9, diff = -1, product = 20, division = 0

BITWISE OPERATOR
The operator which act on the internal bits of respective bytes, are known as
bitwise operator.
C provides 6 bit wise operators for bit manipulation.

& Bitwise and
| Bitwise or
^ Bitwise exclusive or
<< Left shift
>> Right shift
~ one’s complement


& Bitwise-AND operator
The & operator performs a bitwise AND on two integers.

a b a&b
0 0 0
0 1 0
1 0 0
1 1 1
Example: 2&3
2 0000000000000010
3 0000000000000011
2&3 0000000000000010

2

| Bitwise-OR operator
The | (vertical bar) operator performs a bitwise AND on two integers.

a b a|b
0 0 0
0 1 1
1 0 1
1 1 1
Example: 2|3
2 0000000000000010
3 0000000000000011
2|3 0000000000000011

www.opengurukul.com
3 30

^ Bitwise exclusive-OR operator
The ^(caret) operator performs a bitwise AND on two integers.

a b a^b
0 0 0
0 1 1
1 0 1
1 1 0
Example: 2^3
2 0000000000000010
3 0000000000000011
2^3 0000000000000001

1

Operators : Bit-wise : Example
PROGRAM : OUTPUT :
231
#include<stdio.h>
#include<stdlib.h>
int main()
{
printf(“%d %d %d”,
2&3, 2|3, 2^3);
return 0;
}


Left Shift
The shift-left operator (<<, or double left) is used to shift the bit
pattern of a number by a certain number of bits to the left.
Here is an example of shift-left operator:
13<<3=104
13 (00001101)
104 (01101000)


Right Shift
The shift-right operator (>>, or double right) is used to shift this bit
pattern to the opposite direction (right).
Here is another example for the shift-right operator:
52>>4=3
52 (00110100)
3 (00000011)


INCREMENT and DECREMENT
OPERATOR
increment operator ++ adds 1 to its operand.
decrement operator -- subtracts 1 from its operand.

It are two types
1. Pre increment/ Decrement
2. Post increment/ Decrement


Operators : Pre/Post Inc/Dec : Example
PROGRAM:
#include <stdlib.h> x = 11, y = 10
x = 10, y = 10
int main() {
x = 9, y = 10
int x = 10, y; x = 10, y = 10
y = x++; /* y should have 10, x will be 11 post */
printf("x = %d, y = %dn", x, y);
y = --x; /* x will become 10, y will also be 10 */
y = x--; /* y should have 10, x will be 9 post decrement */
y = ++x; /* x will become 10, y will also be 10 */
} www.opengurukul.com 36

Operators : Assignment

It is used to assign the specific value to the variable or constant.

Note: The left hand operand must and should be a variable.

Example:
int x=10;


Operators : Compound Operators

C om pound O p e r a t io n P e r f o r m e d
O p e ra tor
*= Mu ltip lic a tion a s s ig n m e n t
/= D iv is ion a s s ig n m e n t
%= R e m a in d e r a s s ig n m e n t
+= Ad d ition a s s ig n m e n t
-= S u b tra c tion a s s ig n m e n t
<<= L e ft-S h ift a s s ig n m e n t
>>= R ig h t s h ift a s s ig n m e n t
&= B itw is e -A ND a s s ig n m e n t
^= B itw is e -ex c lu s iv e -O R a s s ig n m e n t
|= B itw is e -in c lu s iv e -O R a s s ig n m e n t

Operators : Relational
These operators compare the relation between the specified operands.
If it is true, it will return 1. else returns 0.

Operators Meaning
> Greater than
>= Greater than Equal to
< Lesser than
<= Lesser than Equal to
== Equals
!= Not Equals


Operators : Logical
The operators, generally used in conditional statements.
These operators are used to check between two or more conditions.

Operator Meaning
&& Logical AND
|| Logical OR
! Logical NOT


&& Logical-AND operator

It perform conditional-AND on two boolean expression.

a b a&&b
falsefalse false
falsetrue false
true false false
true true true
Example: 2&&3
2 true
3 true
2&&3 true

1

|| Logical-OR operator

It perform conditional-OR on two boolean expression.

a b a||b
false false false
false true true
true false true
true true true
Example: 2&&0
2 true
0 false
2||0 true

1

! Logical-NOT operator

It performs logical not operation.

a !a
false true
true false

Example: 2(true)
!2->false->0


Operators : Logical : Example
PROGRAM: OUTPUT :
#include<stdio.h> ONE
#include<stdlib.h>
main()
{
if (!1)
printf("NOT ONEn");
else
printf("ONEn");
}


Operators : Comma
The comma operator is a binary operator that evaluates its first
operand and discards the result, it then evaluates the second operand and
returns this value (and type).

int a=1, b=2, c=3, i; // not an operator here
i = (a, b); // stores b into i
i = a, b; // stores a into i
i = (a += 2, a + b); // increases a by 2, then stores a+b = 3+2 into i
i = a += 2, a + b; // increases a by 2, then stores a = 3 into i


Operators : Comma : Example
PROGRAM: OUTPUT :
#include <stdio.h> i = 2, b =2
#include <stdlib.h> i = 1, a =1
int main()
{
int a = 1, b = 2;
int i;
i = (a, b); // stores b into i
printf("i = %d, b =%dn", i, b);
i = a, b; // stores a into i
printf("i = %d, a =%dn", i, a);
return 0;
}

TERNARY OPERATOR
Defines a conditional expression.
In the expression
expr1 ? expr2 : expr3
the expression expr1 is evaluated first.

If it is non-zero(true), then the expression expr2 is evaluated, and that is the
value of conditional expression.

Otherwise, expr3 is evaluated, and that is the value. Only one of expr2 and
expr3 is evaluated.


Operators : Ternary : Example
PROGRAM: OUTPUT :
#include <stdio.h> Enter first value : 3
#include <stdlib.h> Enter second value : 4
main() { Max is : 4
int a, b, max;
printf("Enter first value : ");
scanf("%d", &a);
printf("Enter second value : ");
scanf("%d", &b);
max = (a > b ? a : b);
printf("Max is : %dn", max);
}


Operators : sizeof()
The sizeof() operator can be used PROGRAM :
to figure out size of data type.
#include <stdio.h>
The sizeof() is not a function
whose value determined at run #include <stdlib.h>
time but rather an operator whose int main() {
value is determined by compiler, int i;
So it can be known as compile printf("sizeof i = %d,"
time unary operator. "sizeof(int) = %dn" ,
sizeof (i), sizeof (int));
}

OUTPUT :
sizeof i = 4, sizeof(int) = 4


C Programming

Control Flow


Control structure : Decisions
If-statement
If-else-statement
switch-statement


Control Flow : If Statement
The if statement used to control the flow of execution of
statement.

The general from of a simple if statement is

if ( test expression )
{
statement-block;
}

Control Flow: if Statement : Example
PROGRAM: OUTPUT :
main() { Congratulations!
int grade = 68; You passed!
if (grade > 60)
{
printf(“congratulations!”);
printf(“You passed!”);
}
}


Control flow : if else Statements
The if…else statement is an extension of the simple if statement.
The general from is
if(test expression)
{
true-block statement(s)
}
else
{
false-block statement(s)

Control flow: if else : Example
PROGRAM : OUTPUT :
main() Sorry you failed
{
int grade = 58;
if (grade > 60) {
printf(“congratulations!”);
printf(“You passed!”);
} else {
printf(“Sorry you failed”);
}

Control flow : Switch Statement
Switch allows branching on multiple outcomes.

The general form of the switch statement is

switch (expression)

{

case value-1:

block-1

break;

case value-2:

block-2

break;

……

default:

default-block
break;

Control flow : Switch : Example
PROGRAM:
main() { OUTPUT:

int option = 2; B

switch(option) {
case 1: printf(“A”);
break;
case 2: printf(“B”);
break;
default : printf(“def”);
break;
}
}

Looping control structure
while loop
do-while loop
for loop


Control flow : while Statement

The basic format of the while statement is
while (test condition)
{
body of the loop
}


Control flow : while : Example
PROGRAM: OUTPUT :
main() { 01234
int X = 0;
while ( X < 5 ) {
printf(“ %d ”, X);
X++;
}
}


Control flow : do while Statement

The do while loop takes the following form :
do
{
body of the loop
}
while ( test-condition) ;


Control flow : do while : Example
PROGRAM: OUTPUT :
main() 01234
{
int X = 0;
do
{
printf(“ %d ”, X);
X++;
} while ( X < 5 );

Control Flow : For Statement
The general form of the for loop is

for (initialization; test condition; increment / decrement)
{
body of the loop
}


Control flow : For Loop : Example
PROGRAM: OUTPUT:
main() 01234
{
int i ;
for (i = 0; i < 5; i++)
{
printf(“ %d “,i);
}
}

C Programming

Functions


Functions : Introduction
A block of statements can be grouped together in curly braces { } and given a
name.
It may take parameters as input and can return a value if needed.
The functions are basic building blocks of modular programming language such
as c.
Syntax :
return_type function_name(data_type_1 param1, data_type_2 param2, ...)
{
statement1;
statement2;
return <value>;
}
If the return type is "void", the function doesn't return any value.

Program:
Functions : Example
#include <stdio.h>
sum = add(num1, num2);
int sum(int first, int second)
printf("sum is %dn", sum);
{
}
int total;
Output :
total = first + second ;
sum is 30
return total;
}
void main()
{
int num1 = 10;
int num2 = 20;
int sum; www.opengurukul.com 67

Recursion
Recursion is a programming technique in which function calls
itself.
It repeats the same code, and in some ways it is similar to
looping.


Recursion Example
PROGRAM: int fact(int n) {

#include <stdio.h> int k;

#include <stdlib.h> if (n == 1) return (1);

int main() { else k = n * fact(n - 1);

int n, fact; return (k);

int fact(int); }

printf("nenter the number for which you Output :
want to find the factorialn");
enter the number for which you want to
scanf("%d", &n); find the factorial

fact = fact(n); 5

printf("nthe factorial of the number %d the factorial of the number 5 is 120
is %d", n, fact);
return 0;
}

Function : Calling a function
While calling a parametrized function, we have to pass some
values.
There are two ways to call a function,
1. Call by Value
2. call by Reference.
The difference between these two is:
In case of Call by value the original data will remain unchanged.
But in case of Call by Reference the address is passed to the function
as the parameters, So the original data will changed.


Functions : Call by Value : Example
Program:
Output:
void modify(int,int);
modify: x=100, y=200
void main() {
main: x=10, y=20
int x=10, y=20;
modify(x,y);
printf(“main: x= %d, y= %dn”,x,y);
}
void modify(int x,int y)
{
x=100;
y=200;
printf(“modify: x= %d, y= %dn”,x,y);
}

Functions : Call by Reference : Example

Program: Output:
void modify(int *,int *); modify: x=100, y=200
void main() { main: x=100, y=200
int x=10, y=20;
modify(&x,&y);
printf(“main: x= %d, y= %dn”,x,y);
}
void modify(int *x,int *y)
{
*x=100;
*y=200;
printf(“modify: x= %d, y= %dn”,*x,*y);
}

C Programming

Arrays


Arrays : introduction
1. It is a collection of data of similar data types in a contiguous memory
location.
2. An array can be declared using :
data_type variable_name[size];
3.data_type can be: int, float, char etc
4. An array elements index or subscript begins with number zero.


Arrays : Example
Program:
Output:
#include<stdio.h>
void main() s = hi

{
char s[5]; // declaration of an character Array
s[0]='h'; //initialization of 1st index of the array
s[1]='i';
s[2]='0';
printf(“s = %s”,s); //to print the string
}


Arrays : Array Elements
The syntax for an element of an array called a is a[i]
where i = index of the array element.
In memory, one can picture the array id as in the following
diagram:


Arrays : Initialization
The elements of array can be initialized at the time of declaration
Syntax:
data_type array_name[array size] = {list of values};
Example : initialize array with size
int number[3] = {40, 30, 20};
Will declare an array of size 3.
Will assign 40, 30, 20 to first, second and third element like below.
number[0]=40,
number[1]=30,
number[2]=20 www.opengurukul.com 77

Arrays : Initialization without Size
Example :
initialize array without size (compute automatically)
int counter[] = {101, 102, 103, 104};
Will declare the array to contain four elements with initial values
101, 102, 103 and 104.


Arrays : Example
Program:
#include<stdio.h> Output:
#define MAX_CLASS 5 students in class 1 : 30
Int main() students in class 2 : 35
{
students in class 3 : 40
/* initialize while declaring */
students in class 4 : 45
int students[MAX_CLASS] = {30, 35, 40, 45,
50}; students in class 5 : 50
int class;
for (class = 0; class < MAX_CLASS; class++)
{
printf("students in class %d : %dn", class+1,
students[class]);
}

Arrays : Multidimensional Array
Often there is a need to store and manipulate two dimensional data
structure such as matrices & tables.
Syntax: data_type array_name[num_rows][num_columns];
Example: int holiday[12][31];
Syntax for multidimensional array declaration:
data_type array_name[s1][s2][s3]…..[sn];
Example : int holiday[100][12][31];


Arrays : Multidimensional Array : Example
Program: for(int i=0;i<2;i++)
#include<stdio.h> for(int j=0;j<3;j++)
Void main() Printf(“ x[%d][%d]= %dn“,i,j x[i][j]);
{ }
Int x[2][3]
Output:
Int k=1;
x[0][0] = 1;
for(int i=0;i<2;i++)
X[0][1] = 2;
for(int j=0;j<3;j++)
X[0][2] = 3;
{
x[1][0] = 4;
x[i][j]=k;
X[1][1] = 5;
k++;
X[1][2] = 6;
}
www.opengurukul.com
// for printing all the values of the array 81

Arrays : Array as Parameters
1.An array can also be passed to a function as a parameter by using array
name itself.

2.The base address of an array is passed to the function.

3.The function can use (1) same name or
(2) any other name
to receive the base address of an array.

4.The function can operate on the array passed as a parameter.

5.The changes made to the array in a function will be visible in other
places as it is accessed through pointer.


Arrays : Array as Parameter : Example
PROGRAM:
Output:
#include <stdio.h>
void print_students(int students[], int numstuds) 0:10
{ 1:20
int i; 2:30
for (i = 0; i < numstuds; i++) 3:432
{
printf("%d : %d n", i, students[i]);
}
}
#define NUM_TOPPERS 4
int main()
{
int toppers_roll_no[NUM_TOPPERS] = {10, 20, 30,432};
print_students(toppers_roll_no, NUM_TOPPERS);
return 0;
}

C Programming

Module : Structure


Basics of Structures
A structure is a collection of one or more variables that are
grouped together under a single name. The data type of
variables can be same or different.
The structure is used for convenient handling of related data that
can be grouped together.
The variables that are part of structure are called structure
members or structure fields.
Syntax :
typedef struct emp {
int emp_id;
char emp_name[256];
} emp_t ;
The keyword "struct" is followed by a structure name.

Structures : Access Members/Fields
emp_t e;
defines a variable 'e' which is a structure of the type 'struct
emp'.
The structure members / fields are referred using dot operator '.'
between structure variable and structure field/member.
structure_name.member
Example
e.id
e.emp_name


Structures : Example
/* Example : struct.c */
Output :
#include <stdio.h>
#include <string.h>
$ gcc -o struct struct.c
typedef struct emp {
int emp_id; $ ./struct
char emp_name[256]; id = 432, name = s k
} emp_t ; $
main() {
emp_t e;
e.emp_id = 432;
strcpy(e.emp_name, "S K");
printf("id = %d, name = %sn",
e.emp_id, e.emp_name); www.opengurukul.com 87

}

Pointers to Structure
The pointer to a structure is declared by preceding the variable
name with an asterisk in the declaration.
Access struct members using pointers:
An arrow sign is used to access structure member while
access the data through a pointer to a structure.
pointer_to_structure_variable->structure_member_name
Example:
emp_t *e_p; /* pointer to struct */
e_p->emp_id
e_p->emp_name


Pointers to Structure : Example
/* Example : struct_pointer.c */ main() {
#include <stdio.h> emp_t e;
#include <string.h> emp_t *e_p; /*ptr to struct */
e.emp_id = 432;
typedef struct emp { strcpy(e.emp_name, "sk");
int emp_id; e_p = &e;
char emp_name[256]; printf("id = %d, name = %sn",
} emp_t ; e_p->emp_id,
e_p->emp_name);
}

Self-referential Structure
A structure may have a member whose is same as that of a structure itself. Such
structures are called self-referential.
Self-Referential Structure are one of the most useful features.
They allow you to create data structures that contains references to data of the same
type as themselves.
Self-referential Structure is used in data structure such as binary tree, linked list, stack,
Queue etc.
Example : Single linked list is implemented using following data structures
struct node {
int value;
struct node *next;
};


C Programming

Pointers


Pointers : Introduction
Definition-A pointer is a variable that can hold address of other variables,
structures and functions.
Syntax :
<variable_type> *<name>;
*(de-referencing operator) symbol is used to indicate the pointers.
Example:
int x=10;
ptr x
int *ptr; // pointer to an integer
1000 10
ptr=&x; // ptr contains the address of x
2000 1000
printf(“the value of x is %d“, *ptr); // 10


Pointers : Need of Pointers
These are very efficient to handle the arrays.
Pointers allow C to support dynamic memory allocation.
Pointers provide support to create dynamic data structures
like linked list, stack, queue, etc....
They increase the execution speed, so helps to reduce the
execution time.
Pointers reduce the length and complexity of the programs.
They help to return multiple values in functions.


Pointers : Declaration & Initialization : Example
Program:
#include <stdio.h>
Output:
int main()
x=5
{
int x=5; *p = 5
int *p; &x = 500
p = &x; p = 500
printf(" x= %dn",x); // the value of x
&p = 600
printf("*p = %dn",*p); //the value of x
printf("&x = %un",&x); // the address of x
printf(“ p = %un”,p); // the address of x
printf(“&p = %un”, &p); // the address of the pointer
}

Pointers : Arithmetic Operation
Pointer variable can be used in arithmetic expressions.
For example if p1 and p2 are properly declared and initialized pointers, then the
following statements are valid.
y = *p1 * *p2;
sum = sum + *p1;
z = 5* - *p2/p1;
*p2 = *p2 + 10;
C language allows us to add integers to, subtract integers from pointers as well
as to subtract one pointer from the other,short hand operators with the
pointers p1+=; sum+=*p2; etc.,
Comparison of pointers such as p1 > p2 , p1==p2 and p1!=p2 are allowed.


Address Arithmetic Example
Program:
void main() a = 30, b = 6
{ x = 30
int ptr1,ptr2;
int a,b,x;
a=30;b=6;
ptr1=&a;
ptr2=&b;
x=*ptr1+ *ptr2 –6;
printf("na = %d, b = %dn",a,b);
printf("nx = %d”,x);
}

Pointers : Character pointers in C
In C, string means array of characters. i.e., char a[]=”matsya”;
C does not provide any operators for manipulation of an entire string.
Strings can be manipulated via pointers.
Like 1D arrays, we can use a pointer to access the indivisual characters in a
string.
Generally when we create a string, compiler automatically inserts a null
character(0) at the end.
Example :
char *cp;
m a t s y a 0
cp = “matsya”;

cp


Pointers : Char pointer : Example
Program: Output:
#include<stdio.h> Mataya
void main()
{
char *cptr;
cptr=“Matsya”;
printf(“%s”,cptr);
while(*cptr!=‘0’)
{
if(*cptr==‘s’)
*cptr=‘a’;
printf(“%c”,*cptr);
cptr++;
}

Pointers : Pointers to Arrays
Pointer means address in memory.
Array means group of similar elements in a contiguous memory
location.
If we can keep the track of index element of an array, then by
incrementing the pointer we can obtain the other elements of
the array.
a[0] a[1] a[2]

1 23 45

p


Pointers : Pointers to Array : Example
Program : Output:
# include<stdio.h> a[0] = 1
void main()
p+0 = 1
{
a[1] = 23
int a[]={1,23,45};
p+1 = 23
int *p, i;
p=&a[0]; a[2] = 45
for(i=0;i<3;i++) p+2 = 45
{
printf("a[%d] = %dn",i,a[i]);
printf("p+%d=%dn",i,*(p+i));
}
}

Pointers : Command line arguments

main() function has two arguments.
The first is number of command line arguments i.e., int argc
The second is a pointer to an array of character strings that contain the
arguments one per string i.e., char *argv[]


Command line Argument : Example

Program: cmd.c
bin>tcc cmd.c
#include<stdio.h>
bin>cmd.exe this is a program
main(int argc, char *argv[])
Output:
{
this is a program
int i;
for(i=1;i<argc;i++)
{
printf(“%8s”,argv[i]);
}
}


C Programming

Input & Output


IO : File input & output
The I/O functionality of C is fairly low-level by modern standards; C abstracts all file
operations into operations on streams of bytes, which may be "input streams" or
"output streams".
stdio.h
The standard library functions for file input and output are included in the c standard
library header <stdio.h>
Type
We need a file pointer to read from file and write to a file e.g.:
FILE *fp;
The FILE is an abstract data structure. It includes file descriptor.
Functions
Reading from or writing to a file in C requires 3 basic steps:
Open the file.
Do reading/writing.
Close the file.

Opening a file using fopen
A filepointer is used to open a file present using the format,
FILE* fp;
FILE* fopen(char *name, char *mode);
For opening a file
fp = fopen(name of file, mode);
Mode Normal Access
r Open existing file for "r"eading
w Open file for "w"riting, destroying the contents; create if necessary
a "A"ppend at end of file; create if necessary Update Access (for fixed-length
records)
r+ Open existing file for "r"eading & writing
w+ Open file for reading & "w"riting, destroying the contents; create if necessary
a+ Open file for reading & writing -- all writing is "a"ppended to the end of the file; create
if necessary www.opengurukul.com 105

For checking whether a file exists give
fopen(filename)=NULL;
To read and to write a file, getc and putc are used.
getc returns the next character from a file; it needs the file pointer to tell it which file
int getc(FILE *fp)
getc returns the next character from the stream referred to by fp; it returns EOF for end
of file or error.
putc is an output function :
int putc(int c, FILE *fp)
putc write the character c to the file fp and returns the character written, or EOF if an
error occurs. getc and putc may be macros instead of functions.


getchar and putchar can be defined in terms of getc, putc, stdin, and stdout as
follows:
# define getchar() getc(stdin)
# define putchar(c) putc((c), stdout)
For formatted input or output of files, the functions fscanf and fprints may be
used.
int fscanf(FILE *fp, char *format, ....)
int fprintf(FILE *fp, char *format, ...)
An example program to read characters from console and write that to file and
display that onto console console.


Opening a file using fopen Example
#include <stdio.h> fp = fopen("INPUT", "r");
#include <stdlib.h> while ((c = getc(fp)) != EOF)
int main() { printf("%c", c);
file* fp; fclose(fp);
printf("Data inputn"); return 0;
fp = fopen("INPUT", "w"); }
while ((c = getchar()) != EOF)
putc(c, fp);
fclose(fp);
printf("Data outputn");


Line I/O
fgets
char *fgets(char *line, int maxline, FILE *fp)
The standard library provides an input routine fgets to read a line.
fgets reads the next input line from the file fp into the character array line; at
most maxline-1 characters will be read.
The resulting line is terminated with '0'. Normally fgets returns line; on end of
file or error is returns NULL.
fputs
int fputs(char *line, FILE *fp)
The function fputs writes a string to a file.
It returns EOF if an error occurs, and zero otherwise.
The library functions gets and puts are similar to fgets and fputs, but operate on
stdin and stdout.
gets deletes the terminal 'n', and puts adds it.

Formatted Output using printf
The output function printf translates internal values to characters.
For example
int printf(char *format, arg1, arg2, ......)
printf converts, formats, and prints its arguments on the standard output under
the control of the format.
It returns the number of character printed.
Basic Printf Conversions
--------------------------------------------------------------------------------------------
Character Argument type; Printed as
--------------------------------------------------------------------------------------------
d, i int; decimal number.
o int; unsigned octal number(without leading zero)
x, X int; unsigned hexadecial number without the leading ox or OX.

u int; unsigned decimal number.
c int; single character.
s char *; print character from the string until a '0' or the number of characters
given by the precision.
f double; [-]m.dddddd, where the number of d's is given by the recision
e,E double; print a double in exponential format, rounded, with one digit before
the decimal point, precision after it. A precision of zero suppresses the
decimal point.
There will be at least two digits in the exponent, which is printed as 1.23e15 in
e format, or 1.23E15 in E format.
g, G double; use %e or %E if the exponent is less than -4 or greater than or
equal to the precision; otherwise use %f.
p void *; pointer
www.opengurukul.com
% no argument is converted; print a % 111

A width or precision may be specified as *, in which case the value is computed by
the converting the next argument. For example, to print at most max characters
from a string s,
printf("%.*s", max, s);
Example: printf with various effects
The following table shows the effect of a variety of specifications in printing "hello,
world".
:%s: :hello, world:
:%10s: :hello, world:
:%.10s :hello, wor:
:%-10s: :hello, world:
:%.15s: :hello, world:
:%-15s: :hello, world :
:%15.10s: : hello, wor:
:%-15.10s: :hello,wor :

Formatted Input using scanf
scanf syntax:
scanf(datatype *format, ....);
There is also a function sscanf that reads from a string instead of the standard
input:
int sscanf(char *string, char *format, arg1, arg2, ....)
It scans the string according to the format in 'format', and stores the resulting
values through arg1, arg2, etc.
These arguments must be a pointers.
Basic Scanf Conversions
Character | Input Data | Argument Type
d | decimal integer | int *
u | unsigned decimal integer | unsigned int *
c | character | char *

Error Handling
stderr
The second output stream, called stderr, is assigned to a program in the same
way that stdin and stdout are.
Output written on stderr normally appears on the screen even if the standard
output is redirected.
fprintf(stderr, format, arguments);
The output produced by fprintf goes onto stderr.
It finds it way to the screen instead of disappearing into an output file.
exit
The program uses the standard library function exit, which terminates program
execution when it is called.
The argument of exit is available to whatever process called this one, so the
success or failure of the program can be tested by another program that
www.opengurukul.com
uses this one as a sub process. 115

Char I/O
fgetc()
int fgetc(FILE *fp);
The fgetc function is used to read a character from a stream
If successful, fgetc returns the next byte or character from the stream
If unsuccessful, fgetc returns EOF.
getc()
macro
behaves similar to fgetc()
it may evaluate its arguments more than once.
getchar()
int getchar(void);
function
takes no argument. www.opengurukul.com 116

equivalent to getc(stdin).

Char I/O
fputc()
int fputc(int c, FILE *stream);
The fputc function is used to write a character from a stream to the file
If successful, fputc writes the next byte or character from the stream
If unsuccessful, fgetc returns EOF.


C Programming

Module : Strings


Strings
Strings are defined as an array of characters.
We can used following statement to define a string of 5 characters
char string1[5];
char string2[] = {'A', 'B', 'C', 'D', '0'};
char *string3_p = "ABCD"; /* string literals */
char *string4_p = string2; /* string2 is same as &string2[0] */


String Literals
A string that has been enclosed in double-quotes is called a string literal.
It can be used in place of string variables in the code.
Example :
#include <string.h>
main()
{
char *s_p = "hello"; /* "hello" is a string literal */
printf("%s %sn", s_p, "world"); /* "world" is a string literal */
}
Output: hello world


String Terminator
A special character '0' is used to indicate the end of the string.
This should be stored as a last character of the string.
It is also called as a string null character.
Example :
#include <stdio.h>
int main(void)
{
printf("The character 0 is used to terminate a string.");
return 0;
}
Output: The character

String format specifier
We must use %s to read & print Output:
strings.
Enter your country name :
Example :
india
#include <stdio.h>
You belong to india
#include <string.h>
main()
{
char str[128];
printf("Enter your country name : n");
scanf("%s", str);
printf("You belong to ");
printf("%sn", str);
}

string length : strlen function
The function strlen() can be used to Example: Calculate lengh of string
calculate the length of the string. literals "Hello World"
It doesn't take into account null- #include <string.h>
terminator '0' at the end of the string.
#include <stdio.h>
Example:
main()
length = strlen("hello"); /* should set
length to 5 */ {
int length;
char *message_p = "Hello World";
length = strlen(message_p);
printf("length of %s = %dn",
message_p, length);
}
Output:length
www.opengurukul.com of Hello World = 11 123

string copy : strcpy function
We can copy the contents of one Example : Copy string literal "Hello
string to another using strcpy() World" to a string and display it.
function.
#include <string.h>
Syntax :
#include <stdio.h>
char *strcpy(char *dest, const char
*src); main()
{
char message[128];
strcpy(message, "Hello World");
printf("%sn", message);
}
Output: Hello World


string concatenation : strcat function
We can concatenate contents of one Example :
string to another using strcat()
function. #include <string.h>

Syntax : #include <stdio.h>

char *strcat(char *dest, const char *src); main()
{
char message[128];
strcpy(message, "Hello");
strcat(message, " ");
strcat(message, "World");
printf("%sn", message);
}
Output:Hello World

string compare : strcmp function
We can compare contents of two string to find if they are equal.
The strcmp() takes "case" of the characters into account.
The strcasecmp() ignores case while comparing.
The return value is 0 when the string are equal.
The return value is non-zero when the string are unequal.
Syntax :
#include <string.h>
int strcmp(const char *s1, const char *s2);
int strcasecmp(const char *s1, const char *s2);


string compare: Example
#include <string.h> printf("match case, %s == %s, %dn",
s1, s2, strcmp(s1, s2));
#include <stdio.h>
s1 = "Hello";
main()
s2 = "hello";
{
printf("ignore case, %s == %s, %dn",
char *s1; s1, s2, strcasecmp(s1, s2));
char *s2; }
s1 = "Hello"; Output:
s2 = "Hello"; match case, Hello == Hello, 0
ignore case, Hello == hello, 0


search for string in string : strstr
The function strstr() can be used to search a substring in string.
It returns the pointer that matches the substring.
The NULL pointer is printed as (null) on Linux.

Syntax :
#include <string.h>
char *strstr(const char *haystack, const char *needle);


C Programming

Storage Classes


Scope of Variables
A complete C program need not be compiled all at once; the source text of the
program may be kept in several files, and previously compiled routines may
be loaded from libraries.
If the variable / function has been defined before it use, no declaration is
required.
Otherwise an implicit (for function) / explicit (for variable) declaration is required
before its use.
The same rule applies irrespective of the definition of function/variable in same
source file or another source file.
General rule
- declare all global variables as extern (global) in header file.
- declare all globale functions in header file.
- include the header file in all the source files that needs to access function /
variable.
- each function / variable shouldwww.opengurukul.com
be defined in any one source file 130

External Variables
The program can consists of multiple source files (object files).
For such programs, the variables and functions defined in one file
can be accessed/used in another file.
To ensure that the variables & functions defined in one file are
accessible in another file, you must prefix them with a keyword
"extern" (set external scope) at the time of declaration.
Generally, "extern" is required only for variables.
The functions are implicitly assumed to be "extern" by compiler .
The "extern" declarations are generally done in a common header
file.
The extenal (global) variables are initialized to zero by default by
compiler.

External Variables:Example
Header File : common.h Second Source File : second.c
extern int ev; /* explicit extern */ #include "common.h"
void set_ev(int ); /* implicit extern */ main()
First C Source : first.c {
#include "common.h" printf("ev = %d, ", ev);
int ev; /* definition */ set_ev(5);
void set_ev(int value) printf("ev = %dn", ev);
{ }
ev = value; Compliation & Linking :
} $ gcc -o mexec first.c second.c
Output :
ev = 0,
www.opengurukul.com ev = 5 132

Static Variables
Static storage class is declared with the keyword static as the
class specifier when the variable is defined.
These variables are automatically initialized to zero upon memory
allocation just as external variables are.
Static automatic variables continue to exist even after the block in
which they are defined terminates.
Thus, the value of a static variable in a function is retained
between repeated function calls to the same function.
Static variables may be initialized in their declarations.
Initialization is done only once at compile time when memory is
allocated for the static variable.


Static Variables : Example
PROGRAM: OUTPUT :
#include <stdio.h> 2
#include <stdlib.h> 3
void add() { 4
static int x = 1;
x++;
printf("%dn", x);
}
main() {
add(); // return 2
add(); // return 3
add(); // return 4

Storage Classes : Register
Variables
The register storage class specifier indicates to the compiler that
the object should be stored in a machine register.
Register storage class are used in the hopes of enhancing
performance by minimizing access time and are used when the
variables are frequently used.
An object having the register storage class specifier must be
defined within a block or declared as a parameter to a function.
Objects with the register storage class specifier have automatic
storage duration.
Available when entering the loop and value is gone once exited.
A register variable will be declared as follows:
register int i;

D e f a u lt
TYPE S cope L if e t im e
V a lu e

a u to b od y b od y G a rb a g e v a lu e

s ta tic fu n c tion p rog ra m 0

ex te rn p rog ra m p rog ra m 0

re g is te r b od y b od y G a rb a g e v a lu e


Storage Classes : Initialization
The static and extern variables are initialized to 0 by compiler
An automatic variable remains uninitialized and it will contain
garbage.
You can initialize a variable while defining it.


Storage Classes : Initialization :
Example

extern int i ; /* declaration */
extern int j; /* declaration */
int i = 5; /* definition & initialization */
int j; /* definition * initilization to zero */
main()
{
static int s = 5 ; /* deinition and initializtion to 5 */
static int t ; /* definition and initialization to 0 */
int a; /* definition and uninitizlied - automatic variable */
printf("i = %d, j = %d, s = %d, t = %d, a = %dn", i, j, s,t,a);
}


C Programming

Module
Miscellaneous


The typedef
The typedef statement is used to create a new data type from
existing data types.
We should not use "#define" to refer to data types.
Syntax :
typedef existing_data_type new_data_type;
Example :
typedef unsigned int u_int;
NOTES :
We can use u_int and s_t to declare variables.
u_int i; /* i is a variable of type unsigned int */

Union
A union is a collection of variables that share the same storage.
The union is allocated large enough to hold the value of the largest variable contained in
it.
A union may only be initialized with a value of the type of its first member.
The base address of all the fields of a union is same as they all share the common
storage.
Syntax :
union union_name {
data_type member;
data_type_1 member1;
data_type_2 member2;
};


Union:Access

union-name.member : access union fields using union variable

union-pointer->member : access union fields using pointer to
union variable
Example:


Bit-fields
When Storage space is at premium, it may be necessary to pack several objects into a
single machine word; one common use is a set of single-bit flags in applications like
compiler symbol tables.
Imagine a fragment of a compiler that manipulates a symbol table.The most compact
way to encode such information is a set of one-bit flags in a single char or int.
The usual way this is done to define a set of "masks" corresponding to the relevant bit
position, as in
#define KEYWORD 01
#define EXTERNAL 02
#define STATIC 04
or
enum { KEYWORD = 01 , EXTERNAL = 02 , STATIC = 04 };
The numbers must be powers of two. Then accessing the bits become a matter of "bit-
fiddling" with the shifting, masking, and complementing operators.

Bit-fields
Certain idioms appear frequently:
flags | = EXTERNAL | STATIC;

turns on the EXTERNAL and STATIC bits in flags, while
flags &= -(EXTERNAL | STATIC);

turns them off, and
if((flags & (EXTERNAL | STATIC))==0)....

is true if both bits are off.
A bit-field or field for short, is a set of adjacent bits within a single implementation-defined storage
unit that we will call a "word".
struct {

unsigned int is_keyword : 1;
unsigned int is_extern : 1;

unsigned int is_static : 1;
This defines a variable called flags that contains three 1-bit fields. The number following the colon
represents the field width in bits. The field are declared unsigned int to ensure that they are
unsigned quantities. www.opengurukul.com 144

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