10 arrays and pointers.pptx for array and pointer

UNIT-III Arrays and Pointers W3schools.in, Tutorialspoint.com
Geeksforgeeks.org, codeforwin.org
1
Course : PROGRAMMING IN C
TOPIC: Arrays and Pointers

What is an Array ?
Array is a kind of data structure that can store a fixed-size (finite) sequential
collection of elements of the same (homogeneous) type.
An array is used to store a collection of data, but it is often more useful to think of
an array as a collection of variables of the same type.
To make it simple let's break the words:
• Array is a collection - Array is a container that can hold a collection of
data.
• Array is finite - The collection of data in array is always finite, which is
determined prior to its use.
• Array is sequential - Array stores collection of data sequentially in
memory.
• Array contains homogeneous data - The collection of data in array
must share a same data type.

What is an Array ?
Instead of declaring individual variables, such as number0, number1, ..., and
number99, you declare one array variable such as numbers and use
numbers[0], numbers[1], and ..., numbers[99] to represent individual variables. A
specific element in an array is accessed by an index.
All arrays consist of contiguous memory locations. The lowest address
corresponds to the first element and the highest address to the last element.
We can divide arrays in two categories.
1.One-dimensional array (Or single-dimensional array)
2.Multi-dimensional array

Declaring Array
Declaring Arrays
To declare an array in C, a programmer specifies the type of the elements and
the number of elements required by an array as follows −
This is called a single-dimensional array. The arraySize must be an integer
constant greater than zero and type can be any valid C data type. For example,
to declare a 10-element array called balance of type double, use this statement
−
•type is a valid C data type that must be common to all array elements.
•arrayName is name given to array and must be a valid C identifier.
•arraySize is a constant value that defines array maximum capacity.

Initializing Array
Initializing Arrays
There are two ways to initialize an array.
1.Static array initialization - Initializes all elements of array during its
declaration.
2.Dynamic array initialization - The declared array is initialized some time
later during execution of program.
Static array initialization
We define value of all array elements within a pair of curly braces { and } during
its declaration. Values are separated using comma , and must be of same type.
Note: Size of array is optional when declaring and initializing array at once. The C
compiler automatically determines array size using number of array elements. Hence,
you can write above array initialization as.

Initializing Array

Initializing Array
Initializing Arrays
Dynamic array initialization
You can assign values to an array element dynamically during execution of
program. First declare array with a fixed size. Then use the following syntax to
assign values to an element dynamically.
The array index is an integer value, so instead of
hard-coding you can wrap array input code inside
a loop.

Example: Declaring / Initializing Array
Output

Advantages/ disadvantages of Arrays ?
1. Random access of elements using array index.
2. Use of less line of code as it creates a single array of multiple elements.
3. Easy access to all the elements.
4. Traversal through the array becomes easy using a single loop.
5. Sorting becomes easy as it can be accomplished by writing less line of
code.
Advantages:
1. Allows a fixed number of elements to be entered which is decided at the
time of declaration. Unlike a linked list, an array in C is not dynamic.
2. Insertion and deletion of elements can be costly since the elements are
needed to be managed in accordance with the new memory allocation.
Disadvantages:

Example: To find max and Min number from an array
/* * Find maximum and minimum in all
array elements. */
for(i=1; i<size; i++)
{ /* If current element is greater
than max */
if(arr[i] > max)
{
max = arr[i];
}
/* If current element is smaller
than min */
if(arr[i] < min)
{
min = arr[i];
}
} /* Print maximum and minimum
element */
printf("Maximum element = %dn",
max); printf("Minimum element =
%d", min); return 0;
}
#include <stdio.h>
#define MAX_SIZE 100
// Maximum array size
int main()
{
int arr[MAX_SIZE];
int i, max, min, size;
/* Input size of the array */
printf("Enter size of the array:
"); scanf("%d", &size);
/* Input array elements */
printf("Enter elements in the array:
"); for(i=0; i<size; i++)
{
scanf("%d", &arr[i]);
}
max = arr[0];
min = arr[0];

Example: To find second largest number in an array

Example: To find sum of all array elements
#include <stdio.h>
#define MAX_SIZE 100
int main()
{
int arr[MAX_SIZE];
int i, n, sum=0;
printf("Enter size of the array: "); /* Input size of the array
*/
scanf("%d", &n);
printf("Enter %d elements in the array: ", n);
for(i=0; i<n; i++)
{
scanf("%d", &arr[i]);
}
/* * Add each array element to sum */
for(i=0; i<n; i++)
{
sum = sum + arr[i];
}
printf("Sum of all elements of array = %d", sum);
return 0;
}

Multi-dimensional Array in C
Multi-dimensional array is an array of array or more precisely collection
of array. Unlike one-dimensional array, multi-dimensional array stores.
collection of array.
Let us revise the concept of dimension.
•One-dimensional array : Collection of data/values.
•Two-dimensional array : Collection of one-dimensional array.
•Three-dimensional array : Collection of two-dimensional array.
•N-dimensional array : Collection of N-1 dimensional array.
We can declare array with any dimension. However, two-dimensional
array is most popular and widely used to solve many mathematical
problems.
The simplest form of multidimensional array is the two-dimensional array.
To declare a two-dimensional integer array of size [x][y],

Two dimensional Array in C
Where type can be any valid C data type and arrayName will be a valid C
identifier.
A two-dimensional array can be considered as a table which will have x
number of rows and y number of columns.
A two-dimensional array a, which contains three rows and four columns can
be shown as follows −
Two-dimensional array is a collection of one-dimensional array. Two-
dimensional array has special significance than other array types. We can
logically represent a two-dimensional array as a matrix. Any matrix problem
can be converted easily to a two-dimensional array.

Initializing Two-Dimensional Arrays
Multidimensional arrays may be initialized by specifying bracketed values for
each row. Following is an array with 3 rows and each row has 4 columns.
The nested braces, which indicate the intended row, are optional. The
following initialization is equivalent to the previous example −

Accessing Two-Dimensional Arrays

Example: To Add To matrices

Example: To multiply Two matrices

What is a Pointer ?
Pointers (pointer variables) are special variables that are used to store
addresses rather than values.
Synta
x
Here, we have declared a pointer p of int type which means that p can
store address of any integer value. You can also declare pointers in these
ways.
int* p;
int *p1;
int *
p2;
Let's take another example of declaring pointers.
int* p1,
p2;
Here, we have declared a pointer p1 and a normal variable p2.
Operator
Name
Description
& (address of) Returns the address of a
memory location.
* (indirection) value at (Pointer to a
variable)

What is a Pointer ?
Assigning addresses to Pointers
Example.
Here, 5 is assigned to the c variable. And, the address of c is assigned to
the pc pointer.
To get the value of the thing pointed by the pointers, we use
the * operator. For example
* is called the dereference operator (when working with pointers). It
operates on a pointer and gives the value stored in that pointer

What is a Pointer ?
Let's take one more example.
Initially, the address of c is assigned to the pc pointer using
pc=&c; Since c is 5, *pc gives us 5.
Then, the address of d is assigned to the pc pointer using
pc=&d;. Since d is -15, *pc gives us -15

Example: Working of Pointer
Let's take one more example.
output

Example: Working of Pointer (Explanation)

Passing Array as a Function argument
Way-1
Formal parameters as a pointer −
Way-2
Formal parameters as a sized array −
Way-3
Formal parameters as an unsized array −

Example: Passing Array as a Function argument

Returning Array from a Function
C programming does not allow to return an entire array as an argument to a
function. However, you can return a pointer to an array by specifying the array's
name without an index.
If you want to return a single-dimension array from a function, you would have to
declare a function returning a pointer as in the following example
Second point to remember is that C does not advocate to return the address of
a local variable to outside of the function, so you would have to define the local
variable as static variable.

Returning Array from a Function
consider the following function which will generate 10 random numbers and
return them using an array and call this function as follows:

Pointer to an Array (Relation b/w Array and Pointer)
An array name is a constant pointer to the first element of the array. Therefore,
in the declaration −
balance is a pointer to &balance[0], which is the address of the first element of
the array balance. Thus, the following program fragment assigns p as the
address of the first element of balance −
It is legal to use array names as constant pointers, and vice versa. Therefore,
*(balance + 4) is a legitimate way of accessing the data at balance[4].
Once you store the address of the first element in 'p', you can access the array
elements using *p, *(p+1), *(p+2) and so on. Given below is the example to show
all the concepts discussed above −

In the above example, p is a pointer
to double, which means it can store
the address of a variable of double
type. Once we have the address in
p, *p will give us the value available
at the address stored in p, as we
have shown in the above example.
Pointer to an Array (Relation b/w Array and Pointer)

Modules based upon array and pointers
1. Write suitable array declarations for the following:
a)100 items of integer type
int item[100];
b) A string of 25 characters
char [26];
c) A matrix of order 5 x4
int mat[5][4];
2. Find the output
void main()
{ int a=10, *p, **q;
p=&a; q=&p;
printf(“%d %d %u %u %u”, *p,**q,p,q,*q);
}
Output::
10 10 3616071484 3616071488 3616071484

3. Find the output
a) void main()
{
int i, x[5]={1,2,3,4,5};
for(i=0;i<20;i++)
printf(“n%d”,x[i]);
}
4. Find the output
b) void main()
{
unsigned char var=0;
for(;var>=0;i++)
printf(“n%d”,var);
}

5. Find the output
a) void main()
{
int i=0;
for(;i<9;)
{ i++;
printf(“n%d”,i);
}
}
6. Find the output
b) void fun()
{ if(x>0)
fun(--x);
printf(“n%d”,x);
}
void main()
{ fun(5);
}

7. Find the output
a) void main()
{
int num, *p;
num=5;
p=&num;
printf(“%d”,*p);
}
8. Find the output
b) void main()
{ int I;
static float arr[ ]={1.2,16,34,4.5,45};
for(i=0;i<5;i++)
printf(“n%f”,arr[i]);
}

THANK YOU

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