1. Arrays Topics to cover: Arrays Data Types One-dimensional Arrays
Two-dimensional Arrays

2. Arrays Data Types Data types are of two kinds:
- simple data types (e.g. int, float, double, char)
- Structured data type: (e.g. arrays)
An array is a collection of two or more adjacent memory cells, called array elements, that are associated with a particular symbolic name.
Arrays are of two kinds:
- Arrays of one-dimension
- Arrays of two-dimension

3. One-Dimensional Arrays
Declaration of one-dimension array
Syntax: atype aname [ size ] ; // uninitialized array
atype aname [ size ] = { initialization list } ;
where
atype is any data type;
aname is the name given to the array;
size represents the number of elements in the array.
initialization list is the list of initial values given to the array.

4. One-Dimensional Arrays Examples
EX1: int x [ 3 ];
This tells the compiler to associate 3 memory cells
with name x.
These cells will be adjacent to each other in memory.
Each element of array x contains a value of integer
type
EX2: int Y [ 4 ] = { 2, 4, 6, 8 } ;
This initializes array Y to have 4 elements which contain 2, 4, 6, 8.

5. Accessing One-Dimensional Array
int x [3] ;
Array x in memory:
How to process the data stored in an array?
Syntax:
aname [ index ]
- index is the subscript that is used to reference the desired element.
The array indexing starts from 0 until the fixed size -1. 24 20 10

6. Accessing One-Dimensional Array
Array x in memory:
Index
Values
Accessing the array:
x [0] to access the first element of x
x [1] to access the second element of x
x [2] to access the third element of x 24 20 10

7. Examples on One-Dimensional Arrays
Example1: WriteListOfIntegers
#include <iostream>
using namespace std;
void main () {
int L [5]={1,2,3,4,5};
for (int i=0; i<5; i++)
cout<<L[i] ; }

8. Examples on One-Dimensional Arrays
Example2: ReadListOfIntegers
#include <iostream>
using namespace std;
void main () {
const int ListSize = 10;
int L [ListSize];
cout<<"please enter 10 integer number";
for (int CurElem = 0; CurElem <=9; CurElem++)
cin >> L[CurElem] ; }

9. Examples on One-Dimensional Arrays
Example 3: Write a C++ program that stores the first 5 integers that are multiples of 5 into array A and reads data into array B;computes the sum of the two arrays and stores the result in array C.
# include <iostream.h>
void main ( )
{ int A [5] ; //declaring array A of 5 integers
int B [5] , C [5]; //declaring arrays B and C of 5 integers
for ( int i = 0; i <5 ; i++ )
{ A[ i ] = ( i + 1 ) * 5;
cout << “enter new element in array B”;
cin >> B[ i ] ;
C [ i ] = A[ i ] + B [ i ] ;
cout << C [ i ] << “ “ ;
} }

10. Example3 (Cont.)
The trace of the previous example shows the arrays as follows if B elements are : A B C 5 10 15 20 25 7 6 10 13 23 12 16 25 33 48

11. Example 4
Example 4:
Write a C++ program to read 10 integers and store them in array A. Then it finds the even numbers to store them in array B and the odd numbers to store them in array C.

12. Example 4 (Cont.) // File arrays.cpp #include <iostream.h>
void main ( )
{ int i;
int A [10], B[10], C[10] ;
cout << “ Enter 10 integers : “ ;
for (i = 0 ; i <10; i++)
{ cin >> A[i] ;
if (A[i] % 2 == 0)
B[i] = A[i] ;
else
C[i] = A[i]; }
cout << “B element = “ << “ C element = “ << endl;
for (i = 0; i < 10; i++)
{ cout << B[i] << “ “ << C[i] << endl ;

13. Examples on One-Dimensional Arrays
The resultant arrays B and C in example 2 contain data stored in non consecutive locations in the arrays. Modify the program of example 4 so that the data are stored in consecutive locations.

14. Example 5 (Cont.) / File arrays.cpp #include <iostream.h>
void main ( )
{ int i, j = 0 , k = 0 ;
int A [10], B[10], C[10] ;
for ( i= 0 ; i <10; i++)
{ cin >> A[i] ;
if (A[i] % 2 == 0)
{ B [ j ] = A [ i ] ;
j ++ ; }
else
{ C [k] = A [ i ];
k ++ ; } }
cout << “B element = “ << “ C element = “ << endl ;
for (i=0; i<10; i++)
{ cout << “B[i] << “ “ << “ “ << C[i] << endl ; }

15. Example 6
The problem:
Write C++ program that searches for an integer in array of 10 integers. A proper message should be printed out if the number is found or not.
The Analysis:
A given array of integer numbers is going to be searched in order to find a given number.
Requirements:
Input: an integer number n, an array A of 10 integers
Output: a message “yes found” or “no not found” according to weather the number is found or not.

16. The C++ Program for Example 6
//File search.cpp
#include <iostream.h>
void main ( )
{ int n, i ; int A [ 10 ] ;
bool flag = false;
cout << “ Enter the number that you ant to search for: “ ;
cin >> n ;
cout << “ Enter 10 integers: “ ;
for ( i = 0 ; i < 10 ; i++ )
{ cin >> A[i] ;
if ( A[i] == n )
{ flag = true ; break ; } }
if ( flag == true )
cout << “ Yes, the number is found \n” ;
else cout << “ No, the number is not found \n” ; }

17. Arrays of Two-Dimensions
Syntax ( in C++ ):
atype aname [nrows] [ncolumns] ;
Example:
int B [2] [3] ; // declaring array B of 2 rows and 3 columns
int A [3][3] = {1,2,3,4,5,6,7,8,9}; //initializing array A
Array B in diagram: 1
Reading array B of two-dimensions:
int i , j ;
for ( i = 0 ; i < 2 ; i++ )
for ( j = 0 ; j < 3 ; j++ )
cin >> B[ i ] [ j ] ;

18. Example1 of Two-Dimensional Array
Write a C++ program that reads array A of size (2 x 3) and finds the sum of the elements in each column.
//File arrays2d.cpp
#include <iostream>
using namespace std;
void main ( )
{ int i, j , clmsum = 0 ;
int B[2][3];
cout << "Enter 6 array elements: " ;
for ( i = 0 ; i < 2 ; i++ )
for ( j = 0 ; j < 3 ; j++)
cin >> B[i][j] ;
// Process the array now
{ for ( i = 0 ; i < 2 ; i++ )
clmsum = clmsum + B[i][j] ;
cout << " sum of column no. " << j << " is " << clmsum<<endl;
clmsum = 0; }}

19. Example2 of Two-Dimensional Array
Write a C++ program that reads array B of size (2 x 3) and finds the sum of the elements in each row, and store them in a one-dimensional array of size 2.
//File arrays2d.cpp
#include <iostream>
using namespace std;
void main ( )
{ int i, j , rowsum = 0 ;
int B[2][3], A[2];
cout << "Enter 6 array elements: " ;
for ( i = 0 ; i < 2 ; i++ )
for ( j = 0 ; j < 3 ; j++)
cin >> B[i][j] ;
// Process the array now
for ( i = 0 ; i < 2 ; i++)
{ for ( j = 0 ; j < 3 ; j++ )
rowsum = rowsum + B[i][j] ;
A[i] = rowsum;
rowsum = 0; }}

20. Example3 of Two-Dimensional Array
Write a C++ program that reads an array of size (3 x 3) and finds the product of the left diagonal elements.
//File diagonal.cpp
#include <iostream>
using namespace std;
void main ( )
{ int i, j , product = 1 ;
int B[3][3];
cout << "Enter the 9 array elements: " ;
for ( i = 0 ; i <3 ; i++ )
for ( j = 0 ; j < 3 ; j++)
cin >> B[i][j] ;
// Process the array now
for ( i = 0 ; i < 3 ; i++)
for ( j = 0 ; j < 3 ; j++ )
if ( i == j )
product = product * B[i][j] ;
cout << " The product of the diagonal elements = " << product << endl; }

21. Example3 of Two-Dimensional Array
Anther way to solve Example 3
//File diagonal.cpp
#include <iostream>
using namespace std;
void main ( )
{ int i, j , product = 1 ;
int B[3][3];
cout << "Enter the 9 array elements: " ;
for ( i = 0 ; i <3 ; i++ )
for ( j = 0 ; j < 3 ; j++)
cin >> B[i][j] ;
// Process the array now
for (i=0; i<3;i++)
product*=B[i][i];
cout << " The product of the diagonal elements = " << product << endl; }

22. Example4 of Two-Dimensional Array
Write a C++ program that reads an array of size (3 x 3) and finds the product of the right diagonal elements.
//File diagonal.cpp
#include <iostream>
using namespace std;
void main ( )
{ int i, j , product = 1 ;
int B[3][3];
cout << "Enter the 9 array elements: " ;
for ( i = 0 ; i <3 ; i++ )
for ( j = 0 ; j < 3 ; j++)
cin >> B[i][j] ;
// Process the array now
for ( i = 0 ; i < 3 ; i++)
for ( j = 0 ; j < 3 ; j++ )
if (j == (-1 * i) + 2 )
product = product * B[i][j] ;
cout << " The product of the right diagonal elements = " << product << endl; }

23. Example4 of Two-Dimensional Array
Another way to solve Example4.
//File diagonal.cpp
#include <iostream>
using namespace std;
void main ( )
{ int i, j , product = 1 ;
int B[3][3];
cout << "Enter the 9 array elements: " ;
for ( i = 0 ; i <3 ; i++ )
for ( j = 0 ; j < 3 ; j++)
cin >> B[i][j] ;
// Process the array now
j=2, product=1;
for(int i=0; i<3; i++) {
product*=B[i][j];
j--; }
cout << " The product of the right diagonal elements = " << product << endl; }

24. Example5 of Two-Dimensional Array
Write a C++ program that initializes a 4 X 4 array A, and transpose it into array B.
#include <iostream>
using namespace std;
void main ( )
{ int A[4][4] = {1,2,3,4,5,6,7,8,9,10,11,12,13,14, 15, 16};
int B[4][4];
int i, j;
for (i=0; i<=3;i++)
{ for(j=0;j<=3;j++)
cout<<" "<<A[i][j]<<" ";
cout<<endl; }
cout<<endl<<endl;
for(i=0;i<=3;i++)
for(j=0;j<=3;j++)
B[j][i]=A[i][j];
cout<<" "<<B[i][j]<<" ";
cout<<endl;}
cout<<endl<<endl; }

25. Declaring an array size with an identifier
To declare an array size, you can use a fixed number:
int A[5];
Or a constant:
const arr_size = 10;
int B[arr_size];
But, never a variable, this will cause a syntax error.
To define a dynamic array (i.e. its size is decided during the program execution), you will need to use pointers. This will be discussed later.

26. Array as a parameter in a function
Array name is pointer (call by reference)
When an array is sent to a function as a parameter, it is always a call by reference.
#include <iostream.h>
void Increment (int a[]) {
for (int i=0; i<5; i++)
a[i] += 10; }
void main() {
int b[5] = {10,20,30,40,50};
Increment(b);
for(int i=0; i<5; i++)
cout<<b[i]<<'\t';
cout<<endl; }

27. Array as a parameter in a function
Modify the previous example, so that the function Increment can receive any array of any size.
#include <iostream.h>
void Increment (int a[], int arr_size) {
for (int i=0; i<arr_size; i++)
a[i] += 10; }
void main() {
int b[5] = {10,20,30,40,50};
Increment(b, 5);
for(int i=0; i<5; i++)
cout<<b[i]<<'\t';
cout<<endl; }

28. Array element as a parameter in a function
- Array element as a parameter (call by value). #include <iostream.h> void Inc_element(int a) { ++a; } void main() { int b[5] = {10,20,30,40,50}; Inc_element(b[1]); cout<<b[1]<<endl; }

29. Array element as a parameter in a function
- Array element as a parameter (call by reference). #include <iostream.h> void Inc_element(int &a) { ++a; } void main() { int b[5] = {10,20,30,40,50}; Inc_element(b[1]); cout<<b[1]<<endl; }

30. Swapping two arrays using a function
#include <iostream> using namespace std; void swaparray (int a[], int b[], int arr_size) { int temp; for (int i=0; i<arr_size; i++) { temp = a[i]; a[i] = b[i]; b[i] = temp;} }
void main () { int x[5] = {10,20,30,40,50}; int y[5] = {60,70,80,90,100}; cout << "Before swap "<<endl<<endl<<"Array x"<<endl; for (int i=0; i<5; i++) cout << x[i]<< " "; cout<< endl<<endl<<"Array y"<<endl; for (int j=0; j<5; j++) cout << y[j]<< " "; cout<< endl<<endl; swaparray(x, y, 5); cout << "After swap "<<endl<<endl<<"Array x"<<endl; }

31. Pointer Arithmetic Increment / decrement pointers ( ++ or -- )
Add / subtract an integer to/from a pointer
( + or += , - or -= )
Pointers may be subtracted from each other
Pointer arithmetic is meaningless unless performed on an array

32. Pointer Arithmetic (Cont.)
Example
Consider an integer array V of 5 elements, and an integer pointer vPtr.
Pointer variable vPtr
int *vPtr = V;
//or you can declare it this way.
int *vPtr = &V[0];
vPtr pointes to first element V[0] (location 1000)
i.e. vPtr = 1000
vPtr +=2; sets vPtr to 1008
i.e. vPtr points to V[2]
V[0]
V[1]
V[2]
V[3]
V[4]

33. Pointer Arithmetic (Cont.)
Subtracting pointers
- Returns the number of elements between two
addresses
e.g. if v is an array and
vPtr1 = &v[0];
vPtr2 = &v[2];
then vPtr2 – vPtr1 = 2 (i.e. 2 addresses)

34. Relations Between Pointers and Arrays
Arrays and pointers are closely related.
- Array name is like constant pointer
- Pointers can do array subscribing operations
- If we declare an array A[4] and a pointer aPtr
 aPtr is equal to A
aPtr = A
 aPtr is equal to the address of the first
element of A
aPtr = &A[0]

35. Relations Between Pointers and Arrays (Cont.)
Accessing array elements with pointers:
- Element A[i] can be accessed by *(aPtr+i)
 This is called pointer/offset notation
- Array itself can use pointer arithmetic
 A[3] is same as *(A+3)
- Pointers can be subscripted
(i.e. pointer/subscript notation)
 aPtr [3] is same as A[3]

36. Example1: Pointers as arrays
#include <iostream> using namespace std; void main () { int A[5] = {10,20,30,40,50}; int *p; p= A; cout <<"First element of the array "<<*p<<endl; cout <<"Fourth element of the array "<<*(p+3)<<endl; }

37. Example2: Pointers as arrays
#include <iostream> using namespace std; void main () { int A[5] = {10,20,30,40,50}; int *p; p= &A[0]; for (int i=0; i<5; i++) cout << *(p+i) << " "; cout << endl;} }

38. Example3: Pointers as arrays
#include <iostream> using namespace std; void main () { int A[5] = {10,20,30,40,50}; int *p; p = A; cout << p++ << endl; //this will print the current address of the //pointer, then moves to the next location cout << ++p << endl; //this will move the pointer to the next location //and then prints the new address cout << (*p)++<<endl; //this will print the value that this pointer points //to, and then increment this value }

39. Dynamic Array using Pointers Example1
#include <iostream>
using namespace std;
void main ()
{ int err_size;
cin >> err_size;
int *d = new int[err_size];
for (int i=0; i<err_size; i++)
cin >> d[i];
cout<< endl;
cout << d[i] <<endl; }
err_size
Reading into array
Output

40. Dynamic Array using Pointers Example1: Re-written
#include <iostream>
using namespace std;
void main ()
{ int err_size;
cin >> err_size;
int *d = new int[err_size];
for (int i=0; i<err_size; i++)
cin >> *(d+i);
cout<< endl;
cout << *(d+i) <<endl; }
err_size
Reading into array
The same Output

41. Dynamic Array using Pointers Example2
#include <iostream> using namespace std; void main () { int *p = new int[]; int arr_size = 0; char ch = 'y'; while (ch =='y') { cout << "enter an element"<<endl; cin >> p[arr_size]; //or you can use: cin >> *(p+arr_size); arr_size++; cout << "do you want to continue? (y/n)"<<endl; cin >> ch; } cout <<endl; for (int i=0; i<arr_size; i++) cout<< p[i]<< " "; //or you can use: cout<< *(p+i)<< " ";