1. Dr. Khizar Hayat Associate Prof. of Computer Science
Arrays
Dr. Khizar Hayat
Associate Prof. of Computer Science

2. Arrays
An array is a group of elements of the same data type that are placed in contiguous (adjacent) memory locations.
Each element of the array is identified by an index.
The number of rows/columns of an array are called its dimensions:
One Dimensional Array
Two Dimensional Array

3. Declaring the C++ arrays
One dimensional arrays are declared in C++ by first specifying the data type, then name and then the number of locations in square brackets ([]), e.g.
int varname[50];//declares an integer array of size 50
float real[30];//declares a float array of size 30
char ch[25];//declares a character array of size 25

4. Initializing array
You can declare and initialize arrays in a single statement, e.g.
int foo[5]={16, 2, 77, 40, 12071};
This statement declares an array (named foo) that can be represented like this: 1 2 3 4 16 77 40
12071

5. Initializing array - 2
The number of values between braces, {}, must not be greater than the number of elements. The number may however be lesser, e.g.
int bar[6]={10, 20, 30};
This statement declares an array (named bar) that can be represented like this:
Another example:
int baz[5]={}; 1 2 3 4 5 10 20 30 1 2 3 4
Note that exceeding the element limit is not a syntax error.

6. Accessing the array values
Remember:
int foo[5]={16, 2, 77, 40, 12071};
This array is outlined like below:
Index
Value
The index is also called the subscript. 1 2 3 4
foo[0]
foo[1]
foo[2]
foo[3]
foo[4]

7. Example
#include<iostream> using namespace std; int main () { int a[5]; a[0]=10; a[1]=20; cout<<“Enter the value of 3rd element”<<endl; cin>>a[2]; a[0]=a[0]*5; cout<<a[0]<<“\t”<<a[1]<<“\t”<<a[2]<<endl; return 0; }

8. Accessing array elements: Example
#include<iostream>
using namespace std;
int main () {
int a[10],i;
for (i=0;i<10;i++) //To read and store the inputs
cout<<“Enter the value of <<i<<“th element”<<endl;
cin>>a[i]; }
for (i=0;i<10;i++) //To display the contents of array
cout<<“The value of a[“<<i<<“] is”<<a[i]<<endl;
return 0;
Output at page 8-9 of notes

9. Two-Dimensional Arrays
Two-dimensional Array: a collection of a fixed number of components arranged in two dimensions
All components are of the same type
The syntax for declaring a two-dimensional array is:
dataType arrayName[rowsize][colsize];
where rowsize and colsize are expressions yielding positive integer values

10. Two-Dimensional Arrays (continued)
The two expressions rowsize and colsize specify the number of rows and the number of columns, respectively, in the array
Two-dimensional arrays are sometimes called matrices or tables

12. Two-Dimensional Arrays (continued)
A First Book of C++: From Here To There, Third Edition

13. Accessing Array Components
The syntax to access a component of a two-dimensional array is:
arrayName[indexexp1][indexexp2]
where indexexp1 and indexexp2 are expressions yielding nonnegative integer values
indexexp1 specifies the row position and indexexp2 specifies the column position

15. Processing Two-Dimensional Arrays
A two-dimensional array can be processed in three different ways:
Process the entire array
Process a particular row of the array, called row processing
Process a particular column of the array, called column processing

16. Processing Two-Dimensional Arrays (continued)
Each row and each column of a two- dimensional array is a one-dimensional array
When processing a particular row or column of a two-dimensional array
we use algorithms similar to processing one- dimensional arrays

17. Examples Adding two matrices Multiplying two matrices
Column sums and row sums

18. Strings
A C-style string is a one-dimensional array of characters which is terminated by a null character '\0‘, e.g.
char greeting[6] = {'H','e','l','l','o','\0'};
Another easier way:
char greeting[] = "Hello";
With this type of initialization, no need to place the null character at the end of a string constant.
The C++ compiler automatically places the '\0' at the end of the string when it initializes the array.
In C++, any thing enclosed inside double quotes (“”) is a string of enclosed characters plus ‘\0’

19. Strings: Example
#include <iostream> using namespace std; int main () { char greeting[6]={'H','e','l','l','o','\0'}; cout << "Greeting message: "; cout << greeting << endl; return 0; }

20. Strings: Example
#include <iostream> using namespace std; int main () { char greeting[]=“Hello”; cout << "Greeting message: "; cout << greeting << endl; return 0; }

21. Accessing string elements
You can access elements of a string via for loop and array subscripts but:
Manipulation of Character Arrays or Strings do not require any for loop
You can access the string by just using its identifier (see example - next slide)
Note, However, when giving input to a char array, blank spaces are not allowed.
Blank space in input means the end of array and anything after it will not be stored.

22. Accessing string elements
#include <iostream>
using namespace std;
int main () {
char question[]=“Please, enter your first name:”;
char greeting[]=“Hello ”;
char fname[80];
cout<<question<<endl;
cin>>fname;
cout<<greeting <<“Your first name is…”<<fname<<endl;
return 0; }
Output
Please enter your first name: Asma
Hello Your first name is…Asma

23. String Functions from <cstring>
C++ supports a wide range of functions that manipulate null-terminated strings:
S.N.
Function & Purpose 1
strcpy(s1, s2); Copies string s2 into string s1. 2
strcat(s1, s2); Concatenates string s2 onto the end of string s1. 3
strlen(s1); Returns the length of string s1. 4
strcmp(s1, s2); Returns 0 if s1 and s2 are the same; less than 0 if s1<s2; greater than 0 if s1>s2.