Object Oriented ProgrammingSpring - 2012

COMSATS Institute of Information Technology

Intro to Programming

Kaleem Ullahkaleemullah@ciitvehari.edu.pk

Range of values

• What is the largest integer value that can be expressed in 32 bits?

• How to calculate range? [0…(2n – 1)] For 2 bits? 8 bits?

• For 32-bit computers• from 0 to 4,294,967,295

2

Range of values

• For 32-bit computers• Integer range is from -2,147,483,648 to

2,147,483,647• Integer overflow and underflow

3

What will be the output?

int a=2147483647;cout<<++a;

int a=-2147483648;cout<<a--;cout<<" "<<a;

Range of values

4

What will be the output?

int a=2147483647;cout<<++a; //-2147483648

int a=-2147483648;cout<<a--; //-2147483648cout<<" "<<a; //2147483647

5

Data items• Store data used in program:

read in from user constants used in program

• A data item can be declared either as a constant or a variable Constants are initialized with a value, but

their value cannot be changed after that. The value of a variable can be changed as

needed. • The keyword const in the declaration

indicates that the data item is a constant

6

Examplevoid main(){ // Declaring constants const int MIN_VALUE = 0; const int MAX_VALUE; // Error

MIN_VALUE = 45; // Error

cout << “MIN_VALUE is now “ << MIN_VALUE;

}

7

Declaration of data items.• We need to declare data items in our

program prior to using them.• The declaration tells:

whether the data item is a constant or a variable.

the identifier that will be used in the program to name the data item.

the data type for the data item.

8

Examplevoid main(){ // Declaring a constant. const float PI = 3.1416;

// Single variable declared at a time. int my_number; float GPA; char initial_letter;

// Can declare many data-items of the same type together. int height, base;}

9

Arrays• When we declare variables arbitrary

memory locations are assigned to them• Array

Same type of elements at contiguous location

Same name and type

• To refer to an element, specify Array name and position number

10

Arrays

c[6]

-45

6

0

72

1543

-89

0

62

-3

1

6453

78

Name of array (Note that all elements of this array have the same name, c) c[0]

c[1]c[2]c[3]

c[11]c[10]c[9]c[8]c[7]

c[5]c[4]

Position number of the element within array c

11

Arrays• Format: arrayname[ position number ]

First element at position 0 n element array c:

c[ 0 ], c[ 1 ]…c[ n - 1 ]

• Array elements are like normal variablesc[ 0 ] = 3;cout << c[ 0 ];

• Performing operations in subscript. If x = 3,c[ 5 – 2 ]or c[ 3 ]Or c[ x ]

12

• Total size of an array in bytes?• Total bytes = number of bytes in type x number

of elements• e.g. int sample[10];

Arrays

13

Declaring Arrays

• Declaring arrays - specify: Name Type of array Number of elements Examples

int c[ 10 ]; float hi[ 3284 ];

• Declaring multiple arrays of same type Similar format as other variables Example

int b[ 100 ], x[ 27 ];

14

Getting Values

• int MyArray[5];cin>>MyArray[0];cin>>MyArray[1] ;cin>>MyArray[2] ;cin>>MyArray[3] ;cin>>MyArray[4] ;

• Orfor(int i = 0; i < 5; i++)

cin>>MyArray[i];

15

Examples Using Arrays

• Initializersint n[ 5 ] = { 1, 2, 3, 4, 5 };

If not enough initializers, rightmost elements become 0

If too many initializers, a syntax error is generatedint n[ 5 ] = { 0 };

Sets all the elements to 0• If size omitted, the initializers determine it

int n[] = { 1, 2, 3, 4, 5 };

5 initializers, therefore n is a 5 element array

16

1

2 // Initializing an array with a declaration3 #include <iostream>45 int main()6 {7 int n[ 10 ] = { 32, 27, 64, 18, 95, 14, 90, 70, 60, 37 };89 cout << "Element \t Value" << endl;1011 int i = 0;1213 while(i < 10)14 {15 cout<<i<<“\t”<<n[i];16 i++;17 }18192021 return 0;22}

Notice how they array is declared and elements referenced.

17

int a[10], b[10];

// ...

a = b; // error – illegal

for(int i = 0; i < 10; i++)

a[i] = b[i]; //legal

Arrays

18

• Write a program to input an array of size 10 from the user and Find and print the minimum value in array Find and print the maximum value in array

19

Finding Minimum and Maximumint main(){ int i, min_value, max_value, list[10]; for(i=0; i<10; i++)

cin>>list[i]; // find minimum value min_value = list[0]; for(i=0; i<10; i++) if(min_value>list[i]) min_value = list[i]; cout << "\nminimum value: " << min_value << '\n';// find maximum value max_value = list[0]; for(i=0; i<10; i++) if(max_value<list[i]) max_value = list[i]; cout << "maximum value: " << max_value << '\n'; return 0;}

20

Strings• One dimensional arrays is used to create

character strings• In C++, a string is defined as a character

array that is terminated by a null• A null is specified using ‘\0’• Because of the null terminator, it is

necessary to declare a string to be one character longer

21

Strings• Arrays of characters• All strings end with null ('\0')• Examples

char string1[] = "hello"; Null character implicitly added string1 has 6 elements char string1[] = { 'h', 'e', 'l', 'l', 'o', '\0’ };

• Subscripting is the same string1[ 0 ] is 'h‘ string1[ 2 ] is 'l'

22

Reading strings from keyboard

• The easiest way to read a string entered from the keyboard is to make a character array

int main()

{

char str[80];

cout << "Enter a string: ";

cin >> str; // read string from keyboard

cout << "Here is your string: ";

cout << str<<"\n";

return 0;

}

23

String• Input from keyboard

char string2[ 10 ];cin >> string2;

Puts user input in string• Stops at first whitespace character• Adds null character

If too much text entered, data written beyond array

Printing strings cout << string2 << endl;

• Does not work for other array types

Characters printed until null found

24

Reading strings from keyboard

There is a problem with previous program, if the string has whitespace characters

// Using gets() to read a string from the keyboard.

int main()

{

char str[80];

cout << "Enter a string: ";

gets(str); // read a string from the keyboard

cout << "Here is your string: ";

cout << str<<“\n”;

return 0;

}