Object Oriented Programming Spring - 2012

1. COMSATS Institute of Information Technology Object Oriented ProgrammingSpring - 2012 Intro to Programming KaleemUllah kaleemullah@ciitvehari.edu.pk

2. 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-bitcomputers • from 0 to 4,294,967,295

3. Range of values • For 32-bitcomputers • Integer range is from -2,147,483,648 to 2,147,483,647 • Integer overflow and underflow What will be the output? int a=2147483647; cout<<++a; int a=-2147483648; cout<<a--; cout<<" "<<a;

4. Range of values What will be the output? int a=2147483647; cout<<++a; //-2147483648 int a=-2147483648; cout<<a--; //-2147483648 cout<<" "<<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 constantor 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. Example void 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 todeclaredata 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. Example void main() { // Declaring a constant. const floatPI = 3.1416; // Single variable declared at a time. intmy_number; floatGPA; charinitial_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 Name of array (Note that all elements of this array have the same name, c) c[0] -45 c[1] 6 c[2] 0 c[3] 72 c[4] 1543 c[5] -89 c[6] 0 c[7] 62 c[8] -3 c[9] 1 c[10] 6453 c[11] 78 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 variables • c[ 0 ] = 3; • cout << c[ 0 ]; • Performing operations in subscript. If x = 3, • c[ 5 – 2 ] • or c[ 3 ] • Or c[ x ]

12. Arrays • Total size of an array in bytes? • Total bytes = number of bytes in type x number of elements • e.g. int sample[10];

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] ; • Or for(int i = 0; i < 5; i++) cin>>MyArray[i];

15. Examples Using Arrays • Initializers int n[ 5 ] = { 1, 2, 3, 4, 5 }; • If not enough initializers, rightmost elements become 0 • If too many initializers, a syntax error is generated int 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 declaration Notice how they array is declared and elements referenced. 3 #include <iostream> 4 5 int main() 6 { 7 int n[ 10 ] = { 32, 27, 64, 18, 95, 14, 90, 70, 60, 37 }; 8 9 cout << "Element \t Value" << endl; 10 11 int i = 0; 12 13 while(i < 10) 14 { 15 cout<<i<<“\t”<<n[i]; 16 i++; 17 } 18 19 20 21 return 0; 22 }

17. Arrays int a[10], b[10]; // ... a = b; // error – illegal for(int i = 0; i < 10; i++) a[i] = b[i]; //legal

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 Maximum int main() { inti, 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; }