arrays and pointers

CONTENTS
 Variables
 Placeholders
 Arrays
 Pointers
 Types of Pointers
 Arrays using Pointers

• Variables are simply names used to refer to some location in memory
– a location that holds a value with which we are working.
• Variable names may consists of letters, digits, and the underscore
character subject to the following conditions.
• Eg:- avg,
count ,
emp_salary ,
num1, etc.
Variables

Rules of declaring Variables
• Commas or blanks are not allowed.
• No special characters allowed.
• First letter of the variable should be a letter.
• Uppercase and lowercase letters are significant.
• Variable name should not be a C keyword.
• It should not have same name as the function thst is written by
the user or already exist in the C library.
• Each variable used must be declared in the program.

Placeholders
Placeholders are used to determine when what type of values are going
to be input or displayed, depending on what type of functions that we
use.
Data type Placeholder
int %d
Char %c
float %f
string %s

Input Placeholders:
scanf() function requires input placeholders to allow data to be
transferred to the specific variable depending on which placeholder
we will use.
Output Placeholders:
Output placeholders are used to display data onto the screen. printf()
function uses the output placeholder when necessary. The only
difference with the input placeholders is the double data type
placeholder for input function is %lf, while the double data type
placeholder for output function is %f.

Arrays
 An array is fixed size sequential collection of elements of
homogenous nature.
 Array Declaration:- data_type arrayname[size];
eg- int arr[20]; /*defines a block of 20 consecutive objects of
type int */
 Array Initialization:- int a[5] = { 1,2,3,4,5};
int a[ ] = {1,2,3,4,5};
 Types:- One dimensional
Multi dimensional

One Dimensional Arrays
 A collection of variables are given one variable name using only one
subscript and such a variable is called a single-subscripted variable or
one dimensional array.
 Syntax:- data_type ArrayName[size];
data_type: is a valid data type like int, char, or float.
ArrayName: is a valid identifier.
Size: maximum no. of elements that can be stored in an array.
 Initialization:- int arr[5];
 Stored in contiguous memory locations.

Multi Dimensional Arrays
Two dimensional Array:
 Syntax: data_type ArrayName[rowsize][columnsize];
data_type: is a valid data type like int, char, or float.
ArrayName: is a valid identifier.
rowsize and columnsize : maximum no. of elements that can
be stored in the row and the column.
Initialization:- int arr[2][2];
int arr[2][2] = {1,2,0,1};
int arr[3][3] = {{1,2,0},{1,4,6},{3,8,3}};

Pointers
 A pointer variable is another variable that holds the address of
the given variable to be accessed. Pointers provide a way of
accessing a variable without referring to variable directly.
 Declaration:- type ∗pt_name;
Initialization:- int x, ∗p = & x;
 A pointer should be initialized before use.
 The unary operator ∗ is termed as dereference operator or
indirection operator, as it allows to access the value of a variable
indirectly.

Types Of Pointers
• Null Pointer :- Null pointer is a constant with a value of zero
defined in several standard libraries.
Eg:- int *ptr = NULL
• Dangling Pointers :- If any pointer is pointing to any address at
given point in a program and later on the variable has been
deleted from that specific memory location, although the pointer
is still referring to the memory location. These pointers are called
dangling pointers.
Eg :- int *x,* y;
x = (int *)malloc(sizeof (int));
*y=10;
x = y;
free (y);

• GenericPointers :- Pointers which doesn’t have any specific data
type is known as generic pointers.
Eg :- void *the_data;
• Wild Pointers :- Uninitialized pointers are known as wild
pointers because they point to some arbitrary memory location
and may cause a program to crash or behave badly.
Eg:- int main ( )
{
int *ptr;
printf(“%d”,*ptr);
}

#include <stdio.h>
int main()
{
int data[5], i;
printf("Enter elements: ");
for(i = 0; i < 5; ++i)
scanf("%d", data + i);
printf("You entered: n");
for(i = 0; i < 5; ++i)
printf("%dn", *(data + i));
return 0;
}
Arrays Using Pointers
Output :
Enter elements: 1
2
3
5
4
You entered: 1
2
3
5
4

Difference between Arrays and
Pointers
POINTERS
ARRAY
Pointer is a variable which stores
the address of another variable.
Array is a collectihon of
homogeneous data elements.
Pointer can’t be initialized at
definition.
Arrays can be initialized at
definition.
They are static in nature. They are static in nature.
The assembly code of pointer is
different that array.
The assembly code of an array is
different than pointer.

arrays and pointers

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arrays and pointers