Data structure array

Data Structure using C++
Lecturer
Majid Hamid Ali
2020 - 2021
Tikrit University
Collageof ComputerScienceandMathematics

Arrays
1. One-Dimensional Arrays
2. Accessing Array Elements
3. Representation of Arrays in Memory
4. Example: Finding the Maximum
5. No Array-to-Array Assignments

NEED FOR AN ARRAY
 To store large number of variables of same type under a
single variable.
 Easy understanding of the program.
 E.g.
To store Marks of 50 students.
Record of sales of 100 salesman.

Represent a Linear Array in memory
 The elements of linear array are stored in consecutive
memory locations. It is shown below:

WHAT IS AN ARRAY
 An array is a derived data type ( derived from
fundamental data type )
 It is a collection of variables of the same type that are
referenced by a common name.
 Consist of contiguous memory locations.
 Lowest address corresponds to first element
 Highest address corresponds to the last element.
 Can have data items of type like: int, char, float and
also user-defined types like : structures, objects.

Accessing Array Elements
 An individual element within an array is
accessed by use of an index.
 An index describes the position of an
element within an array.
 Note: In C++ the first element has the
index zero!

Representation of Arrays in Memory
In C++, any array is mapped to a contiguous
memory location.
All memory elements reside next to each
other.

One-Dimensional Arrays
A one-dimensional array is a list of related variables.
The general form of a one-dimensional array declaration
is:
Data type Array_name [size];
• Data type: base type of the array,
determines the data type of each element in the array
• size: how many elements the array will hold
• variable_name: the name of the array
Examples:
int sample[10];
float float_numbers[100];
char last_name[40];

Memory Representation of Single Dimension
Array
 If the array is float arr [ 5 ];
memory representation would be as follows:
Arr [ 0 ] Arr [ 1 ] Arr [ 2 ] Arr [ 3 ] Arr [ 4 ]
5016
5012
5008
5004
5000
Total Memory requirement is : size of ( type ) * size of array 4*5 = 20 bytes

ARRAY INITIALISATION
int list [ 5 ] ; // declaration
int list [ 5 ] = { 10, 20, 30, 40, 50 } ;
// declaration & initialization

UNSIZED ARRAY INITIALISATION
 Can skip the size of an array in array initialization
 Elements of an array can be added or removed
without changing array dimensions.
E.g.
float price [ ] = { 50.5, 63.97, 84.6, 779.8 };

for ( i = 0 ; i < 10 ; i + + )
{
cout << a [ i ] << endl;
}
// display the 10 elements of the array

// replay.cpp
// gets four ages from user, displays them
#include <iostream>
using namespace std;
int main()
{
int age[4]; //array ‘age’ of 4 ints
for(int j=0; j<4; j++) //get 4 ages
{
cout << “Enter an age: “;
cin >> age[j]; //access array element
}
for(j=0; j<4; j++) //display 4 ages
cout << “You entered “ << age[j] << endl;
return 0;
}

Example:
int a[8];
int j;
for(j=0; j<8; j++)
a[j] = 7-j;
Then the memory representation of array a
looks like this:

Example: Finding the Maximum
#include <iostream.h>
int main()
{
int i, max = 0;
int list[100];
// initialize the array with random values
for(i=0; i<100; i++)
list[i] = rand();
// find maximum value
for(i=0; i<100; i++)
if(max < list[i])
max = list[i];
cout << “Maximum value: “ << max;
return(0);
}

No Array-to-Array Assignments
You cannot assign one array to another in C++.
The following is illegal:
int a[10], b[10];
// do something
// assign all elements of array b to array a
a = b; // error -- illegal
Instead, you have to do the assignments for each
element:
int i;
// assign all elements of array b to array a
for(i=0; i<10; i++)
a[i] = b[i];

For example, you can compile and run the
following program, even though the array crash
is being overrun:
// An incorrect program. Do not execute!
int main()
{
int crash[10], i;
for(i=0; i<100; i++) crash[i] = i;
return(1);
}

Creating an Array
void main( )
{
int a[10]; // declaration of an array ‘a’
int n;
// input 10 elements in an array
for ( n = 0; n < 10 ; n + +)
{
cin >> a [ n ];
}
// display the 10 elements of the array input
for ( n = 0 ; n < 10 ; n + + )
{
cout << a [ n ] << endl;
}
}

Program to count the no. of employees earning more than Rs. 1 lakh per
annum. Monthly salaries of 10 employees are given.
void main ( )
{
const int size = 10 ;
float sal [ size ] , an_sal ;
int count = 0;
// loop to accept monthly salaries of 10 employees
for ( int j = 0 ; j < size ; j + + )
{
cout << “ Enter the monthly salary of employee “ << j + 1 ;
cin >> sal [ j ];
}

// loop to count employees earning more than Rs. 1 lakh per annum
for ( j = 0 ; j < size ; j + + )
{
an_sal = sal [ j ] * 12 ;
if ( an_sal > 100000 )
{
count ++ ;
}
}
cout << count << “ employees out of “ << size << “ employees are
earning more than Rs. 1 lakh per annum “ ;
}

WAP to input 10 numbers in an array and replace all even
no.s by 0 and odd no.s by 1
void main ( )
{
int a [ 10 ], n;
// loop to accept 10 values in an array ‘a’
for ( n = 0; n < 10 ; n + +)
{
cin >> a [ n ];
}
// loop to check if the element of an array is even replace by 0
// and if odd replace by 1
for ( n = 0; n < 10 ; n + +)
{
if ( ( a [ n ] % 2 ) == 0 )
{
a [ n ] = 0;
}
else
{
a [ n ] = 1 ;
} } }

WAP to find the largest and smallest no. in an array of 10 elements
// input an array
// display the array
// to find the largest element
int largest = a [ 0 ] ;
for ( int i = 1 ; i < 10 ; i + + )
{
if ( a [ i ] > largest )
{
largest = a [ i ];
}
}
cout << “ largest value is : “ << largest ;

WAP to find the largest and smallest no. in an array of 10 elements
// input an array
// display the array
// to find the lowest element
int lowest = a [ 0 ];
for ( n = 1 ; n < 10 ; n + + )
{
if ( a [ n ] < lowest )
{
lowest = a [ n ];
}
}
cout << “ lowest value is : “ << lowest ;

Two-Dimensional Arrays
A two-dimensional array is a list of one-dimensional arrays.
To declare a two-dimensional integer array two_dim of size 10,20 we
would write:
int matrix[3][4];
This corresponds to a table with 3 rows and 4 columns (for example).

We can generate the array above by using
this program:
#include <iostream.h>
int main()
{
int row=3, col=4;
int matrix[row][col];
for(row=0; row < 3; ++row) {
for(col=0; col < 4; ++col) {
matrix[row][col] = (row*4)+ col +1;
cout << matrix[row][col] << ‘ ‘;
}
cout << ‘n’;
}
return(0);}

Memory Allocation for Two-Dimensional Arrays
 Storage for all array elements is determined at compile time.
 The memory used to hold an array is required the entire time that
the array is in existence.
 The following formula determines the number of bytes of memory
that will be allocated:
bytes = rows * columns * number_of_bytes_in_type
 For example, an integer array (with two-byte integers) with
dimensions 100,100 would require 100 * 100 * 2 = 20,000 bytes.

Aggregate Operations
Aggregate operations on arrays are not allowed in C++. Given
int arrayOne[20];
int arrayTwo[20];
arrayOne = arrayTwo; // assignment - not allowed
if(arrayOne == arrayTwo) // comparison - not allowed
cout << arrayOne; // output - not allowed (except C-strings)
cin >> arrayOne; // input - not allowed (except C-strings)
arrayTwo = arrayTwo - arrayOne; // arithmetic - not allowed
return arrayOne; // returning an entire array - not allowed
SomeFunc(arrayTwo); // pass as an argument to a function - allowed

Advantages of Array:
 It is used to represent multiple data items of same
type by using single name.
 It can be used to implement other data structures
like linked lists, stacks, queues, tree, graphs etc.
 Two-dimensional arrays are used to represent
matrices.
 Many databases include one-dimensional arrays
whose elements are records.

Disadvantages of Array
 We must know in advance the how many elements are to be
stored in array.
 Array is static structure. It means that array is of fixed size.
The memory which is allocated to array cannot be increased
or decreased.
 Array is fixed size; if we allocate more memory than
requirement then the memory space will be wasted.
 The elements of array are stored in consecutive memory
locations. So insertion and deletion are very difficult and
time consuming.

Accessing to data
1.Sequential.
2.Computed address.
3.Linked address.

Sequential
 This method is slow because the access to record take
long time
 sequential reading from first record to last record
especially when the file size is large
 the record to be searched at the end of the file.

Computed address
One dimension array
LOC( A[I] ) = LO + I

One dimension array
Ex :- find location of A[4] from array has size (20) where base
address = 100?
LOC( A[I] ) = LO + I
LOC( A[4] ) = 100 + 4
=100+4
=104

Tow dimension
Row wise method
LOC( A[I] [J] ) = LO + N * I + J
B. Colum wise method
LOC( A[I] [J] ) = LO + M * J + I

Tow dimension
• LO = Base address
• I = Row subscript of element whose address is
to be found
• J = Column subscript of element whose
address is to be found
• M = Number of row of the given matrix
• N = Number of column of the given matrix

Tow dimension
Ex :- find location of ( A[1] [2]) from matrix is stored in
col_ wise method where A array
A [3] [3] and base address=500?
LOC( A[I] [J] ) = LO +M*J + I
( A[1] [2])= 500+3*2+1
= 500+7
= 507

Three dimension array
int z[n1] [n2] [n3]
A. Row wise method
LOC( z[i1] [i2] [i3] ) = LO + n2 * n3 * i1 + n3 * i2 + i3
LOC(z[i1] [i2] [i3]) = LO + i1 + n1 * i2 + n1 * n2 * i3

Let X : box[9][6] [8] of integer
Compute the location of the element box[5][3][6] using Row-wise and
column- wise when the base address is 1200.
n1= 9 n2= 6 n3= 8 i1= 5 i2= 3 i3= 6
A.Row wise method
LOC( box[i1] [i2] [i3] ) = LO + n2 * n3 * i1 + n3 * i2 + i3
LOC( box[5] [3] [6] ) = 1200 + 6 * 8 * 5 + 8 * 3 + 6
= 1200+ 240 + 24+6
= 1470

LOC(z[i1] [i2] [i3]) = LO + i1 + n1 * i2 + n1 * n2 * i3
LOC( box[5] [3] [6] ) = 1200 + 5 + 9* 3 + 9 * 6 * 6
= 1200+5 + 27+324
= 1556
n1= 9 n2= 6 n3= 8 i1= 5 i2= 3 i3= 6

Data structure array

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