1. Today’s Objectives 28-Jun-2006 Announcements
Midterm Exam answers will be posted on the discussion group page
Review Quiz #2 and Midterm Exam
Class string and String Stream Processing (Ch. 18)
String assignment and concatenation
Comparing strings
Substrings
Finding and replacing characters in a string
Conversion to C-Style strings
String stream processing
Getting input from the keyboard with embedded white space
Demo – A Simple Library Application (Continued)

2. Review Quiz #2 and Midterm Exam

3. Progress Review

4. So far, we have learned… Progress Review Object-Oriented Programming
Basics of C++
Functions and argument passing
Arrays
Pointers and dynamic memory allocation
C++ classes and objects
Some C++ standard libraries and their namespace
The STL vector class
Programs that use objects to solve problems
Debugging techniques
Object-Oriented Design
A simple software process
Pseudocode algorithms
UML class diagrams and use case diagrams

5. Next… The string class and the stringstream class Operator overloading
Progress Review
Next…
The string class and the stringstream class
Operator overloading
Inheritance
Polymorphism
Templates
Stream I/O
Exception handling
File processing
Linked lists
The g++ compiler

6. Class string and String Stream Processing
Chapter 18

7. Class string and String Stream Processing (Deitel, 884–906)
C++ string class is an object-oriented approach to strings
#include <string> using std::string;
Creating a string object
string s1;
string s2("Test");
string s3 = "Test";
Finding the length
int len = s2.length(); //len is 4

8. String Assignment Assigning Accessing individual chars
Class string and String Stream Processing (Deitel, 884–906)
String Assignment
Assigning
string s1, s2 = "Test";
s1 = s2;
s1.assign(s2); //Same as s1 = s2
Accessing individual chars
s2[0] = 'R'; //Changed to "Rest"
s2.at(0) = 'B'; //Changed to "Best"

9. String Concatenation Use operator + with strings and chars
Class string and String Stream Processing (Deitel, 884–906)
String Concatenation
Use operator + with strings and chars
string s1 = "Hello";
string s2 = "World";
s1 += ", ";
string s3 = s1 + s2 + '!';
Use the append function
string s4;
s4.append( s3, 0, 5 );
cout << s4; //Prints "Hello"

10. Class string and String Stream Processing (Deitel, 884–906)
Comparing strings
C++ strings can be compared with ==, !=, <, >, <=, and >=
string s1 = "Hello", s2 = "World";
if( s1 == s2 ) cout << "equal";
Also with the compare function
int result = s1.compare(s2);
result is 0 if s1 is equal to s2
result is a positive number if s1 is lexicographically greater than s2
result is a negative number if s1 is lexicographically less than s2
Comparing substrings
int result = s1.compare( 0, 1, s2, 0, 1 );
This example compares the first char of s1 to the first char of s2

11. Substrings Use the substr function to extract a substring
Class string and String Stream Processing (Deitel, 884–906)
Substrings
Use the substr function to extract a substring
string s1 = "Hello, World!";
string s2 = s1.substr( 0, 5 );
Index of the starting char
Length of the substring

12. Finding and Replacing chars
Class string and String Stream Processing (Deitel, 884–906)
Finding and Replacing chars
Using find()
string s1 = "It was the worst of times.";
int pos = s1.find("worst");
if( pos == string::npos ) cout << "Not found";
else cout << "Found at position " << pos;
Using replace()
s1.replace( pos, 5, "best" );
Replacement string
Index of the starting char
Number of chars to replace

13. Conversion to C-Style Strings
Class string and String Stream Processing (Deitel, 884–906)
Conversion to C-Style Strings
Use the c_str function
string s1 = "Hello";
const char *ps1 = s1.c_str();

14. String Stream Processing
Class string and String Stream Processing (Deitel, 884–906)
String Stream Processing
Input from strings – ostringstream class
Output to strings – istringstream class
Both input and output – stringstream class
#include <sstream> using namespace std;
Member function that returns a string
stringstream ss;
ss.str();

15. Applications of String Streams
Class string and String Stream Processing (Deitel, 884–906)
Applications of String Streams
Use << to insert data to be printed to an ostringstream object, and then print it later, Fig page 903
Example: convert int or double data to a string
int i = 42;
stringstream ss;
ss << i;
string s = ss.str();

16. Using cin to Get Input Containing Whitespace

17. Get a String Containing Whitespace
Using cin (Lippman)
Get a String Containing Whitespace
cout << "Enter your first and last name: ";
const int BUFFSIZE = 1024;
char buffer[BUFFSIZE];
cin.getline(buffer,BUFFSIZE);
cout << buffer << endl;
//Or create a string
string s = string(buffer);
Gets input from the keyboard up to the \n, and puts this input into the char array, including the whitespace

18. Potential Problem Using cin char input;
cout << "Enter your selection: ";
cin >> input;
cin.ignore();//Sometimes needed if you use cin first
cout << "Enter the title: ";
const int BUFFSIZE = 1024;
char buffer[BUFFSIZE];
cin.getline( buffer, BUFFSIZE );
string title = string(buffer);

19. Checking for Input Errors with cin

20. Problem: User Enters Wrong Datatype
Checking for errors with cin
Problem: User Enters Wrong Datatype
int input;
cout << "Enter the number of copies: ";
cin >> input;
while( !cin ){
cin.clear();
cin.ignore();
cout << "That was not an integer, try again: "; }
If the user enters a char here, then the value of “input” will be unusable

21. Problem: User Enters Wrong Datatype
Checking for errors with cin
Problem: User Enters Wrong Datatype
int input;
cout << "Enter the number of copies: ";
cin >> input;
while( !cin ){
cin.clear();
cin.ignore();
cout << "That was not an integer, try again: "; }
We test whether the user entered the wrong datatype, with “!cin”.
If “!cin” is true, then we have to clear the cin object and ignore the next byte.

22. A Simple Library Application (Continued)
Demo
A Simple Library Application (Continued)

23. Library Demo Progress review TODO
Implemented two classes in the first version
Book class
BookList class
TODO
Implement the Library class

24. References
Deitel, H. M., and P. J. Deitel, C++ How to Program, Fifth Edition. Upper Saddle River, NJ: Prentice Hall, 2005.