C programming

C Language
Wednesday, November 19, 2014 H1arshit

Overview of C
• C is developed by Dennis Ritchie
• C is a structured programming language
• C supports functions that enables easy
maintainability of code, by breaking large file into
smaller modules
• Comments in C provides easy readability
• C is a powerful language
2

Program structure
A sample C Program
#include<stdio.h>
int main()
{
--other statements
// Comments after double slash
}
3

C Character set
• C uses
• Uppercase letters A to Z
• Lowercase letters a to z
• Digits: 0 to 9
• Special Characters:
• + - ! # % ^ & * ? <>;.’|?/”
• Special combination
• b- backspace
• n- New Line
• t- horizontal tab
• a- print with alert
Wednesday, November 19, 24014

Header files
• The files that are specified in the include section is
called as header file
• These are precompiled files that has some functions
defined in them
• We can call those functions in our program by
supplying parameters
• Header file is given an extension .h
• C Source file is given an extension .c
` 5

Identifiers
• Identifiers are the name given to various elements
such as variables, functions and array.
• Both upper and lower case letters are permitted
• May begin with _ (underscore)
• Diff b/w - and _

Main function
• This is the entry point of a program
• When a file is executed, the start point is the main
function
• From main function the flow goes as per the
programmers choice.
• There may or may not be other functions written by
user in a program
• Main function is compulsory for any c program
7

Writing the first program
#include<stdio.h>
int main()
{
printf(“Hello”);
return 0;
}
• This program prints Hello on the screen when we
execute it
8

Running a C Program
• Type a program
• Save it
• Compile the program – This will generate an exe file
(executable)
• Run the program (Actually the exe created out of
compilation will run and not the .c file)
• In different compiler we have different option for
compiling and running. We give only the concepts.
9

Comments in C
• Single line comment
• // (double slash)
• Termination of comment is by pressing enter key
• Multi line comment
/*….
…….*/
This can span over to multiple lines
` 10

Data types in C
• Primitive data types
• int, float, double, char
• Aggregate data types
• Arrays come under this category
• Arrays can contain collection of int or float or char or
double data
• User defined data types
• Structures and enum fall under this category.
11

Variables
• Variables are data that will keep on changing
• Declaration
<<Data type>> <<variable name>>;
int a;
• Definition
<<varname>>=<<value>>;
a=10;
• Usage
<<varname>>
a=a+1; //increments the value of a by 1
12

Variable names- Rules
• Should not be a reserved word like int etc..
• Should start with a letter or an underscore(_)
• Can contain letters, numbers or underscore.
• No other special characters are allowed including
space
• Variable names are case sensitive
• A and a are different.
13

Keywords
• In C there are certain reserved word that we cannot
declare as variable.
• These word is known as keyword
• Keywords are reserved words that have a special
meaning in a programming language.
Wednesday, November 19,1 24014

Keywords
• auto
• double
•• break
int
•struct
• else
•long
•switch
• case
• enum
•register
•typedef
• char
• extern
•return
•union
• const
• float
•short
•unsigned
• continue
• for
•signed
•void
• • default
goto
•sizeof
•volatile
• if
•static
•• do while
15

Input and Output
• Input
• scanf(“%d”,&a);
• Gets an integer value from the user and stores it under the
name “a”
• Output
• printf(“%d”,a);
• Prints the value present in variable a on the screen
16

For loops
• The syntax of for loop is
for(initialisation;condition checking;increment)
{
set of statements
}
Eg: Program to print Hello 10 times
for(I=0;I<10;I++)
{
printf(“Hello”);
}
17

While loop
• The syntax for while loop
while(condn)
{
statements;
}
Eg:
a=10;
while(a != 0) Output: 10987654321
{
printf(“%d”,a);
a--;
}
18

Do While loop
• The syntax of do while loop
do
{
set of statements
}while(condn);
Eg:
i=10; Output:
do 10987654321
{
printf(“%d”,i);
i--;
}while(i!=0)
19

Conditional statements
if (condition)
{
stmt 1; //Executes if Condition is true
}
else
{
stmt 2; //Executes if condition is false
}
20

Conditional statement
switch(var)
{
case 1: //if var=1 this case executes
stmt;
break;
case 2: //if var=2 this case executes
stmt;
break;
default: //if var is something else this will execute
stmt;
}
21

Operators
• Arithmetic (+,-,*,/,%)
• Relational (<,>,<=,>=,==,!=)
• Logical (&&,||,!)
• Bitwise (&,|)
• Assignment (=)
• Compound assignment(+=,*=,-=,/=,%=,&=,|=)
• Shift (right shift >>, left shift <<)
22

String functions
• strlen(str) – To find length of string str
• strrev(str) – Reverses the string str as rts
• strcat(str1,str2) – Appends str2 to str1 and returns
str1
• strcpy(st1,st2) – copies the content of st2 to st1
• strcmp(s1,s2) – Compares the two string s1 and s2
• strcmpi(s1,s2) – Case insensitive comparison of
strings
23

Numeric functions
• pow(n,x) – evaluates n^x
• ceil(1.3) – Returns 2
• floor(1.3) – Returns 1
• abs(num) – Returns absolute value
• log(x) - Logarithmic value
• sin(x)
• cos(x)
• tan(x)
24

Procedures
• Procedure is a function whose return type is void
• Functions will have return types int, char, double,
float or even structs and arrays
• Return type is the data type of the value that is
returned to the calling point after the called function
execution completes
25

Functions and Parameters
• Syntax of function
Declaration section
<<Returntype>> funname(parameter list);
Definition section
<<Returntype>> funname(parameter list)
{
body of the function
}
Function Call
Funname(parameter); Wednesday, November 192, 62014

Example function
#include<stdio.h>
void fun(int a); //declaration
int main()
{
fun(10); //Call
}
void fun(int x) //definition
{
printf(“%d”,x);
}
27

Actual and Formal parameters
• Actual parameters are those that are used during a
function call
• Formal parameters are those that are used in function
definition and function declaration
28

Arrays
• Arrays fall under aggregate data type
• Aggregate – More than 1
• Arrays are collection of data that belong to same data
type
• Arrays are collection of homogeneous data
• Array elements can be accessed by its position in the
array called as index
29

Arrays
• Array index starts with zero
• The last index in an array is num – 1 where num is the
no of elements in a array
• int a[5] is an array that stores 5 integers
• a[0] is the first element where as a[4] is the fifth element
• We can also have arrays with more than one dimension
• float a[5][5] is a two dimensional array. It can store 5x5
= 25 floating point numbers
• The bounds are a[0][0] to a[4][4] 30

Structures
• Structures are user defined data types
• It is a collection of heterogeneous data
• It can have integer, float, double or character data in
it
• We can also have array of structures
struct <<structname>>
{
members;
}element;
We can access element.members;
31

Structures
struct Person
{
int id;
char name[5];
}P1;
P1.id = 1;
P1.name = “vasu”;
32

Type def
• The typedef operator is used for creating alias of a
data type
• For example I have this statement
typedef int integer;
Now I can use integer in place of int
i.e instead of declaring int a;, I can use
integer a;
This is applied for structures too.
33

Pointers
• Pointer is a special variable that stores address of
another variable
• Addresses are integers. Hence pointer stores integer
data
• Size of pointer = size of int
• Pointer that stores address of integer variable is
called as integer pointer and is declared as int *ip;
34

Pointers
• Pointers that store address of a double, char and
float are called as double pointer, character pointer
and float pointer respectively.
• char *cp
• float *fp
• double *dp;
• Assigning value to a pointer
int *ip = &a; //a is an int already declared
35

Examples
int a;
a=10; //a stores 10
int *ip;
ip = &a;//ip stores address of a (say 1000)
ip : fetches 1000
*ip : fetches 10
* Is called as dereferencing operator
36

Call by Value
• Calling a function with parameters passed as
values
int a=10; void fun(int a)
fun(a); {
defn;
}
Here fun(a) is a call by value.
Any modification done with in the function is local
to it and will not be effected outside the function

Call by reference
• Calling a function by passing pointers as parameters
(address of variables is passed instead of variables)
int a=1; void fun(int *x)
fun(&a); {
defn;
}
Any modification done to variable a will effect outside
the function also
38

Example program – Call by value
#include<stdio.h>
void main()
{
int a=10;
printf(“%d”,a); a=10
fun(a);
}
void fun(int x)
{
printf(“%d”,x) x=10
x++;
printf(“%d”,x); x=11
}
39

Explanation

Example Program – Call by
reference
#include<stdio.h>
void main()
{
int a=10;
fun(a);
}
void fun(int x)
{
printf(“%d”,x) x=10
x++;
printf(“%d”,x); x=11
}

Explanation
a and x are referring to same location. So
value will be over written.

Conclusion
• Call by value => copying value of variable in another
variable. So any change made in the copy will not
affect the original location.
• Call by reference => Creating link for the parameter
to the original location. Since the address is same,
changes to the parameter will refer to original
location and the value will be over written.

C programming

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