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Variables
Variable is the name of a memory
location which stores some data.
25 S
a b
Memory

Variables
Rules
a. Variables are case sensitive
b. 1st character is alphabet or '_'
c. no comma/blank space
d. No other symbol other than '_'

Constants
Values that don't change(fixed)
Types
Integer
Constants
Character
Constants
Real
Constants
1, 2, 3, 0
, -1, -2 1.0, 2.0,
3.14, -24
'a', 'b', 'A',
'#', '&'

32 Keywords in C
Keywords
Reserved words that have special
meaning to the compiler

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

Program Structure
#include<stdio.h>
int main() {
printf("Hello World");
return 0;
}

Comments
Single Line Multiple
Line
Lines that are not part of program
//
/*
*/

Output
printf(" Hello World ");
printf(" kuch bhi n");
new line

Output
printf(" age is %d ", age);
printf(" value of pi is %f ", pi);
printf(" star looks like this %c ", star);
CASES
integers
1.
2. real numbers
3. characters

Compilation
Hello.c C Compiler
A computer program that translates C code
into machine code
a.exe (windows)
a.out (linux & mac)

Instructions
These are statements in a Program
Types
Type Declaration
Instructions
Control
Instructions
Arithmetic
Instructions

Instructions
Type Declaration Instructions Declare var before using it
int a = 22;
int b = a;
int c = b + 1;
int d = 1, e;
VALID INVALID
int a = 22;
int b = a;
int c = b + 2;
int d = 2, e;
int a,b,c;
a = b = c = 1;
int a,b,c = 1;

Arithmetic Instructions
a + b
Operand 1 Operand 2
Operator
NOTE - single variable on the LHS

a = b + c
VALID INVALID
b + c = a
a = bc
a = b^c
a = b * c
a = b / c
NOTE - pow(x,y) for x to the power y

Modular Operator %
Returns remainder for int
3 % 2 = 1
-3 % 2 = -1

Type Conversion
int int
op int
int float
op
op
float
float float float

Operator Precedence
*, /, %
+, -
=
x = 4 + 9 * 10
x = 4 * 3 / 6 * 2

Associativity (for same precedence)
Left to Right
x = 4 * 3 / 6 * 2

Instructions
Control Instructions
Used to determine flow of program
a. Sequence Control
b. Decision Control
d. Case Control
c. Loop Control

Operators
a. Arithmetic Operators
b. Relational Operators
d. Bitwise Operators
c. Logical Operators
e. Assignment Operators
f. Ternary Operator

Operators
==
>, >=
<, <=
!=
Relational Operators

Operators
&& AND
|| OR
! NOT
Logical Operators

Operator Precendence
Priority
1
2
3
4
5
6
7
8
Operator
!
*, /, %
+, -
<, <=, >, >=
==, !=
&&
||
=

Operators
=
+=
-=
Assignment Operators
*=
/=
%=

Conditional Statements
Types
if-else Switch

if-else
if(Condition) {
//do something if TRUE
}
else {
//do something if FALSE
}
Ele is optional block
can also work without {}

else if
if(Condition 1) {
//do something if TRUE
}
else if (Condition 2) {
//do something if 1st is FALSE & 2nd is TRUE
}

Conditional Operators
Condition ? doSomething if TRUE : doSomething if FALSE;
give 1 & 0 cases
Ternary

switch(number) {
case C1: //do something
break;
case C2 : //do something
break;
default : //do something
}
switch

a. Cases can be in any order
switch Properties
b. Nested switch (switch inside switch) are allowed

Loop Control Instructions
Types
for do while
while
To repeat some parts of the program

for Loop
for(initialisation; condition; updation) {
//do something
}

- Increment Operator
Special Things
- Decrement Operator
- Loop counter can be float
or even character
- Infinite Loop

while(condition) {
//do something
}
while Loop

do {
//do something
} while(condition);
do while Loop

skip to next iteration
continue Statement

Nested Loops
for( .. ) {
for( .. ) {
}
}

Take
Argument
Do
Work
Return
Result
block of code that performs particular task
Functions
increase code reusability
it can be used multiple times

Function Prototype
Syntax
void printHello( );
> Tell the compiler
1

Function Definition
Syntax
printf("Hello");
void printHello() {
}
2
> Do the Work

Syntax
Function Call
int main() {
return 0;
}
printHello( );
3
> Use the Work

- Execution always starts from main
Properties
- A function gets called directly or indirectly from main
- There can be multiple functions in a program

Function Types
Library
function
User-
defined
Special functions
inbuilt in C
declared & defined by
programmer
scanf( ), printf( )

Passing Arguments
functions can take value & give some value
parameter return value

Passing Arguments
void printHello( );
void printTable(int n);
int sum(int a, int b);

Argument v/s Parameter
values that are
passed in
function call
values in function
declaration &
definition
used to send
value
used to receive
value
actual
parameter
formal
parameters

NOTE
a. Function can only return one value at a time
b. Changes to parameters in function don't change the values in
calling function.
Because a copy of argument is passed to the function

Recursion
When a function calls itself, it's called recursion

a. Anything that can be done with Iteration, can be done with
recursion and vice-versa.
Properties of Recursion
b. Recursion can sometimes give the most simple solution.
d. Iteration has infinite loop & Recursion has stack overflow
c. Base Case is the condition which stops recursion.

Pointers
A variable that stores the memory
address of another variable
22
age
Memory
2010
ptr
2010
2013

Syntax
int age = 22;
int *ptr = &age;
int _age = *ptr;
22
age
Memory
2010
ptr
2010
2013

Declaring Pointers
int *ptr;
char *ptr;
float *ptr;

Format Specifier
printf("%p", &age);
printf("%p", ptr);
printf("%p", &ptr);

Pointer to Pointer
A variable that stores the memory
address of another pointer
22
age
Memory
2010
ptr
2010
2013
pptr
2013
2012

Pointer to Pointer
Syntax
int **pptr;
char **pptr;
float **pptr;

Pointers in Function Call
Call by
Value
call by
Reference
We pass value of
variable as
argument
We pass address of
variable as
argument

Arrays
Collection of similar data types stored at
contiguous memory locations

Syntax
int marks[3];
char name[10];
float price[2];

Input & Output
scanf("%d", &marks[0]);
printf("%d", marks[0]);

Inititalization of Array
int marks[ ] = {97, 98, 89};
int marks[ 3 ] = {97, 98, 89};
Memory Reserved :

Pointer Arithmetic
Pointer can be incremented
& decremented
CASE 1

Pointer Arithmetic
CASE 2
CASE 3

Pointer Arithmetic
- We can also subtract one pointer from another
- We can also compare 2 pointers

Array is a Pointer
int *ptr = &arr[0];
int *ptr = arr;

Traverse an Array
int aadhar[10];
int *ptr = &aadhar[0];

Arrays as Function Argument
printNumbers(arr, n);
void printNumbers (int arr[ ], int n)
void printNumbers (int *arr, int n)
OR
//Function Declaration
//Function Call

Multidimensional Arrays
arr[0][0]
2 D Arrays
int arr[ ][ ] = { {1, 2}, {3, 4} }; //Declare
//Access
arr[0][1]
arr[1][0]
arr[1][1]

Strings
A character array terminated by a '0' (null character)
null character denotes string termination
EXAMPLE
char name[ ] = {'S', 'H', 'R', 'A', 'D', 'H', 'A','0'};
char class[ ] = {'A', 'P', 'N', 'A', ' ', 'C', 'O', 'L', 'L', 'E', 'G', 'E', '0'};

Initialising Strings
char class[ ] = {'A', 'P', 'N', 'A', ' ', 'C', 'O', 'L', 'L', 'E', 'G', 'E', '0'};
char name[ ] = "SHRADHA";
char class[ ] = "APNA COLLEGE";

What Happens in Memory?
char name[ ] = "SHRADHA";
2000
name
S H R A D H A 0
2001 2002 2003 2004 2005 2006 2007

String Format Specifier
"%s"
printf("%s", name);
char name[ ] = "Shradha";

IMPORTANT
scanf( ) cannot input multi-word strings with spaces
Here,
gets( ) & puts( ) come into picture

String Functions
gets(str)
input a string
(even multiword)
puts(str)
output a string
fgets( str, n, file)
Dangerous &
Outdated
stops when n-1
chars input or new
line is entered

String using Pointers
char *str = "Hello World";
Store string in memory & the assigned
address is stored in the char pointer 'str'
char *str = "Hello World";
char str[ ] = "Hello World";
//cannot be reinitialized
//can be reinitialized

Standard Library Functions
1 strlen(str)
count number of characters excluding '0'
<string.h>

2 strcpy(newStr, oldStr)
copies value of old string to new string
<string.h>

3 strcat(firstStr, secStr)
concatenates first string with second string
<string.h>
firstStr should be large
enough

4 strcpm(firstStr, secStr)
Compares 2 strings & returns a value
<string.h>
0 -> string equal
positive -> first > second (ASCII)
negative -> first < second (ASCII)

Structures
a collection of values of different data types
EXAMPLE
name (String)
For a student store the following :
roll no (Integer)
cgpa (Float)

Syntax
struct student {
char name[100];
int roll;
float cgpa;
};
struct student s1;
s1.cgpa = 7.5;

Syntax
struct student {
char name[100];
int roll;
float cgpa;
}

Structures in Memory
struct student {
char name[100];
int roll;
float cgpa;
}
name
2010
cgpa
2114
2110
roll
structures are stored in contiguous memory locations

Benefits of using Structures
- Good data management/organization
- Saves us from creating too many variables

Array of Structures
struct student COE[100];
struct student ECE[100];
struct student IT[100];
IT[0].roll = 200;
ACCESS
IT[0].cgpa = 7.6;

Initializing Structures
struct student s1 = { "shradha", 1664, 7.9};
struct student s2 = { "rajat", 1552, 8.3};
struct student s3 = { 0 };

Pointers to Structures
struct student *ptr;
ptr =&s1;
struct student s1;

Arrow Operator
(*ptr).code ptr->code

Passing structure to function
void printInfo(struct student s1);
//Function Prototype

typedef Keyword
used to create alias for data types
coe student1;

File IO
- RAM is volatile
FILE - container in a storage device to store data
- Contents are lost when program terminates
- Files are used to persist the data

Operation on Files
Create a File
Open a File
Close a File
Read from a File
Write in a File

Types of Files
Text Files
.exe, .mp3, .jpg
Binary Files
textual data
.txt, .c
binary data

File Pointer
FILE is a (hidden)structure that needs to be created for opening a file
A FILE ptr that points to this structure & is used to
access the file.
FILE *fptr;

Opening a File
fptr = fopen("filename", mode);
FILE *fptr;
Closing a File
fclose(fptr);

File Opening Modes
open to read
"r"
open to read in binary
"rb"
open to write
"w"
open to write in binary
"wb"
open to append
"a"

BEST Practice
Check if a file exists before reading from it.

Reading from a file
fscanf(fptr, "%c", &ch);
char ch;

Writing to a file
fprintf(fptr, "%c", ch);
char ch = 'A';

Read & Write a char
fgetc(fptr)
fputc( 'A', fptr)

EOF (End Of File)
fgetc returns EOF to show that the file has ended

Dynamic Memory Allocation
It is a way to allocate memory to a data structure during
the runtime.
We need some functions to allocate
& free memory dynamically.

Functions for DMA
a. malloc( )
b. calloc( )
c. free( )
d. realloc( )

malloc( )
takes number of bytes to be allocated
& returns a pointer of type void
ptr = (*int) malloc(5 * sizeof(int));
memory allocation

calloc( )
initializes with 0
ptr = (*int) calloc(5, sizeof(int));
continuous allocation

free( )
We use it to free memory that is allocated
using malloc & calloc
free(ptr);

realloc( )
reallocate (increase or decrease) memory
using the same pointer & size.
ptr = realloc(ptr, newSize);

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