Object-Oriented Programming
Object-Oriented Programming (COM357J)
Lecture Week 5
Arrays and Pointers
An array is a set of data of the same type having common name. A particular
data element is accessed by a subscript specified in brackets after array name.
Example
10, 12, 13, 9, 2, 17 are values of integer type.
The set of values is referred to as an array and the individual values are called
elements and can be specified as follows
x[0]
x[1]
x[2]
x[3]
x[4]
x[5]
10
12
13
9
2
17
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Object-Oriented Programming
x is an array of 6 elements of integer type.
The elements 10, 12, 13, 9, 2, 17 are specified by the subscripts [0] through [5]
respectively.
Like all other programming languages, C++ provides arrays of following
dimensions
 One-dimensional array
 Two- dimensional array
 Multidimensional array
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Object-Oriented Programming
One-dimensional arrays
A list of data items can be given a variable name with one subscript.
Such an array is called one-dimensional array.
Syntax
type array_name[size];
Type can be any base type and size defines the number of elements in the
array.
All arrays have as subscript of their first element.
Example
int x[6];
char p[10];
x is an integer type array with 6 elements, x[0] through x[5].
p is a character type array with 10 characters, p[0] through p[9].
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Object-Oriented Programming
Example
/* Simple example of an array */
void main()
{
int x[5];
int element, t;
for(t=0;t<=4;t++)
{
cout<< “Enter value of element ” << t << “\n”;
cin >>element;
x[t] = element;
}
for(t=0;t<=4;t++)
cout<< “x[“<<t<<”] = ” <<x[t];
getch();
}
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Object-Oriented Programming
Storage locations are reserved by the declaration.
The subscript of an array can be integer constants, integer variables or
expressions that yield integers.
Example
x[5]
x[t]
x[strlen(p)]
x[i+j]
The elements may be used in programs just like any other C++ variables.
Example
a = x[0]+5;
x[4] = x[1] + x[2];
x[2] = x[5] + y[1];
Value[5] = x[i]*3;
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Object-Oriented Programming
C++ language treats character strings simply as arrays of characters.
Each character is an element of the array.
Example
char name[6];
The name can be of maximum 6 characters long.
Let the name be ABDUL. It will be stored as follows.
Name [0]
Name [1]
Name [2]
Name [3]
Name [4]
Name [5]
‘A’
‘B’
‘D’
‘U’
‘L’
‘\0’
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Object-Oriented Programming
When a compiler sees a character string, it terminates it with an additional null
Character.
Thus, the element Name[5] holds the null character ”\0’” at the end.
For example, name[5] can mean John’\0’
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Object-Oriented Programming
Example
/* Example of character array*/
# include <ctype.h>
main( )
{
char name[10];
int i ;
cout<< “Enter your name \n”;
cin>>name;
cout<< “Your name in upper case letter\n”;
i=0;
while(name[i] != ‘\0’)
{
cout<< toupper(name[i]);
i++;
}
cout<< “\n”;
}
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Object-Oriented Programming
Initialization of arrays
The elements of arrays can be initialized in the same way as ordinary
variables.
The general form of initialization of arrays is as follows
static type array_name[size]={list of values};
The values in the list are separated by comma.
Example
static float p[4]={1.7,2.5};
In the example, the elements are assigned values like p[0]=1.7, p[1]=2.5 and
p[2] and p[3] will be assigned 0.
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Object-Oriented Programming
In the declaration, size may be omitted only when every element is initialized.
Example
static int R[ ]={1,3,5,6};
Character arrays may be initialized in the similar way.
Example
static char name[ ]={‘A’,’B’,’D’,’U’,’L’};
There is no shortcut method for initializing a large number of array elements.
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Object-Oriented Programming
To initialize such an array, it would be better to use loop.
Example
int array_large[100];
for(t=0;t<100;t++)
{
if(t>50)
array_large[t]=1;
else
array_large[t]=0;
}
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Object-Oriented Programming
Example l6x13.cpp
/* Example of an array, Finding the largest and the smallest
element in the vector */
void main()
{
int t,n;
float a[50], large, small;
cout<< “Size of the vector :: ”;
cin<<n;
cout<< “\n”<<n;
for(t=0;t<n;t++)
{cout<< “Enter elements of vector” << t << “\n”;
cin>>a[t];
}
large =a[0];
/* initialize value to small and large element */
small = a[0];
/* finding the smallest and largest elements */
for(t=0;t<n;t++)
{
if(a[t]>large)
large =a[t];
else if(a[t]<small)
small =a[t];
}
cout<< “Largest element in vector is = \n” <<large;
cout<< “Smallest element in vector is = \n”<<small;
getch();
}
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Object-Oriented Programming
Two –dimensional arrays
A two-dimensional array, in essence, is an array of one-dimensional arrays i.e.
it can be viewed as a matrix consisting of rows and columns.
Example
a11
a21
a31
a12 a13
a22 a23
a32 a33
In mathematics, we represent a particular element in a matrix by two
subscripts such as aij
a denotes the matrix and aij represents the element in the i-th row and in the
j-th column.
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Object-Oriented Programming
In C/C++, a matrix can be defined by using two-dimensional array.
Syntax
type array_name [row_size][column_size];
Each dimension of the array uses a subscript from 0 through n-1, where n is
the size of the row or column.
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Object-Oriented Programming
Example - l6x8.cpp
/* Example of a two-dimensional array */
void main()
{
int i,j, matrix[3][4];
cout<< “Enter values of the elements of the matrix \n”;
for(i=0;i<3;i++)
for(j=0;j<4;j++)
cin>>matrix[i][j];
/* display the elements */
for(i=0;i<3;i++)
{
for(j=0;j<4;j++)
cout<< matrix[i][j];
cout<< “\n”;
}
}
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Object-Oriented Programming
Initializing two-dimensional arrays
The elements of arrays can be initialized in the same way as one-dimensional
arrays.
The general form of initialization of two-dimensional arrays is as follows
static type array_name[size][size]={list of values };
Initialization is done row by row and commas separate the values in the list.
Example
static int matrix [2][3] ={1,5,6,2,9,11};
One pair of braces can separate the rows.
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Object-Oriented Programming
A two dimensional array can also be initialized in the form of a matrix.
Commas are required after each brace that closes off a row, except for the last
row of the matrix.
If the values are missing in an initialize, they are automatically set to zero.
Example
static int table[2][3]= {{1,7,3}, {4,2,8}};
It can be written in matrix form as follows
static int matrix[3][3]= {{1,2,3},
{4,5,6},
{7,8,9}};
Missing values are set to zero.
static int matrix[2][3] ={1,5,7};
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Object-Oriented Programming
When all the elements are to be initialized to zero, the following shortcut
method can be used.
Example
static int matrix[3][3]={{0},
{0},
{0}};
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Object-Oriented Programming
Example
/* Example of two dimensional array_adding two arrays */
#include<stdio.h>
void main()
{
int A[3][3],B[3][3],C[3][3];
int t,j,m,n;
/* Initialize matrix A */
for(t=0;t<3;t++)
for(j=0;j<3;j++)
cin>>A[t][j];
/* Print matrix A in matrix form */
for(t=0;t<3;t++)
{
for(j=0;j<3;j++)
cout<<A[t][j];
cout<< “\n”;
}
cout<< “\n”;
/* Initialize matrix B */
for(m=0;m<3;m++)
for(n=0;n<3;n++)
cin>>B[m][n];
/* Print matrix B in matrix form */
for(m=0;m<3;m++)
{
for(n=0;n<3;n++)
cout<< B[m][n];
cout<< “\n”;
}
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Object-Oriented Programming
cout<< “\n”;
/* cheek if the matrix can be added */
if(t==m && j==n)
{
for(t=0;t<m;t++)
for(j=0;j<n;j++)
C[t][j] = A[t][j] +B[t][j];
cout<< “Sum of matrices A and B :: \n”;
for(t=0;t<m;t++)
{
for(j=0;j<n;j++)
cout<<C[t][j];
cout<< “\n”;
}
cout<< “\n”;
}
else
cout<< “The two matrix cannot be added.\n”;
}
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Object-Oriented Programming
Multidimensional array
Arrays of more than two dimensions are refereed to as multidimensional array.
Arrays of more than three dimensions are rarely used because of the amount of
memory required to hold them.
Syntax
type array_name[size1][size2]…..[sizeN]
Example
int x[3][2][4];
A three dimensional array is layers of two-dimensional array.
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Object-Oriented Programming
Example
int x[3][2][2];
The array x can be visualized as
1
1
1
3
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2
4
2
2
Object-Oriented Programming
Character strings as arrays
The most common use of one-dimensional arrays is character strings.
Any group of characters enclosed with double quotation marks is a constant
string.
The character strings are normally terminated by a null character, specified as
‘\0’.
Example
“Muchacha”
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Object-Oriented Programming
This is an array of 9 characters including a null character ‘\0’ at the end of the
string as shown below.
‘M’ ‘u’ ‘c’ ‘h’ ‘a’ ‘c’ ‘h’ ‘a’ ‘\0’
Character strings are declared as arrays. The general form is as follows
char string_name[size];
The size should be equal to the number of characters plus one for the null
character.
Example
char name[10];
Character strings may be initialized when they are declared with the general
form as follows
static char string_name ={string};
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Object-Oriented Programming
Example
static char city[7]={“London”};
It is the same as the following
static char city[7]={‘L’,’o’,’n’,’d’,’o’,’n’,’\0’};
If an array is completely initialized, then its dimension does not need to be
specified.
Example
static char city[ ]={“Sheffield”};
static int marks[ ]={45,47,61,55};
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Object-Oriented Programming
Pointers
A pointer contains a memory address.
This address is the location of another variable in memory.
For example
Address
5010
Variable
217
Price
5012
5014
5010
int price=217;
&price=5010;
ptr=&price;
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Ptr
Object-Oriented Programming
A pointer enables programmer to access a variable that is defined outside the
function.
Pointers increase the execution speed.
Use of pointer array to character string saves data storage space in memory.
Pointers reduce length and complexity of a program e.g. linked list, graphs,
binary tree etc.
Declaration, Initialization and Accessing pointers
Syntax
data_type *pointer_name;
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Object-Oriented Programming
The following things are done by the above declaration
 Tells that pointer_name is a pointer variable.
 Pointer_name is associated with memory location.
 Data_type denotes a base type.
Example
int price=217;
int *ptr;
//declared
ptr= &price; //must be initialised
*ptr= price=217;
A pointer must be initialized with the address of a variable before the pointer
can be used.
The general form of pointer initialization is as follows:
pointer_name =&variable_name;
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Object-Oriented Programming
Example
int price=217;
int *ptr;
ptr= &price;
Initialization of a pointer with an absolute address is prohibited.
Example
ptr=5010;
/* Not valid */
A pointer can be initialized in its declaration itself. Declare variable first!
Example
int prince, *ptr=&price; /* valid */
int ptr=&price;
/* not valid */
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Object-Oriented Programming
Example
char string[10];
char *ptr =string;
This assigns the starting address of the character array to ptr.
Value of a variable can be accessed by using the pointer and this is done by
unary operator *(asterisk) usually known as indirection operator.
Example
int price=217, value;
int *ptr;
ptr= &price; /* ptr points to address of variable price */
value = *ptr; /* *ptr yeilds the contents of address */
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Object-Oriented Programming
Pointer expressions
Pointer variables can be used in expressions like ordinary variables.
Example
x= (*p) * (*q);
y= *p - *q;
*p= *p+10;
p++;
/* points to the memory location of the next element */
--q;
sum +=*p;
p =p+1;
It is possible to compare two pointers in a relational expression.
Example
if(p<q)
printf(“P points to lower memory location than q \n”);
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Object-Oriented Programming
Example
for(;ptr<=&x[4];ptr++)
printf(“%x[%d] %d %d ”,i , *ptr, ptr);
Example
while(*ptr)
printf(“%c”,*ptr++);
Pointer and array
Example (Prg L6x13.cpp)
/* Example of pointers and array */
#include<stdio.h>
void main()
{
int sum,t;
int *ptr;
static int x[5]={1,2,3,4,5};
ptr=x; /*Starting address of array is assigned to ptr */
sum=0; t=0;
printf(“Element
value
address \n”);
for( ; ptr<=&x[4]; ptr++,t++)
{
printf(“ x[%d]
%d
%u \n”,t,*ptr,ptr);
sum +=*ptr;
}
cout<<“\n” << “Sum = ” << sum;
}
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Object-Oriented Programming
Example –(Prg L6x14.cpp)
/* Example of pointer and arrays, finding the smallest
element in an array */
void main(){
int small, i;
int *ptr;
int x[5];
cout<<“Enter elements of array ::\n”;
for(i=0;i<5;i++)
cin>>x[t]);
ptr= x; /* ptr =&x[0] */
small =*ptr;
ptr++;
for(i=1;i<5;i++)
{
if(small>*ptr)
small= *ptr;
ptr++;
}
cout<<“The smallest number is ”<<small;
getch();
}
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Object-Oriented Programming
Example (Prg L6x15.cpp)
/* Example of pointer and character strings */
#include<stdio.h>
void main()
{
char string[10], *ptr;
ptr= string;
cout<<"Enter a string :: \n";
gets(string);
while(*ptr)
cout<<*ptr++;
getch();
}
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Object-Oriented Programming




Pointers in functions as parameters
Address of a variable can be passed as parameter to a function in a normal
fashion.
When passing addresses to a function, the parameters receiving the
addresses should be pointers.
Process of calling a function using pointers to pass the address of variable is
known as call by reference.
General form is as follows
main()
{
…….
func(&x,&y);
……….
}
func(type *p, type *q)
{
……….
}
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Object-Oriented Programming
The following points should be noted
 Formal parameters should be declared as
pointer.
 When function is called, the addresses are
passed as actual parameters (call by
reference).
Example L6x19.cpp
void func( int *);
main()
{
int x=20;
cout<< "Call of function by reference \n";
func(&x);
cout<< "\n";
getche();
}
void func(int *p)
{
int a=5;
*p=*p+a;
cout << "\n a = " << a;
cout << "\n p = "<< *p;
}
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Object-Oriented Programming
Example L6X17.cpp
double disc(int *, int *, int *);
void main()
{
int a=2, b=2, c=2;
double d;
d=disc(&a,&b,&c);
cout<<"discreminant " << d <<"\n\n";
getche();
}
double disc(int *a, int *b, int *c)
{
double *s;
*s=(*b)*(*b)-4*(*a)*(*c);
return *s;
}
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Object-Oriented Programming
Pointer parameters are commonly used in string functions. Notice, for string
array address sign is not required.
Example (l6x18.cpp)
void copy(char *, char *);
main() {
char name1[10] ,name2[10];
cout<< "Enter name2 :: \n";
cin>>name2;
copy(name1, name2);
cout<< "Copied name is " <<name1;
getche();
}
void copy(char *s1, char *s2)
{
while((*s1++ = *s2++) != '\0')
;
}
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