1. Introduction to C++ Version 1.1

2. Topics C++ Structure Primitive Data Types I/O Casting Strings Control Flow

3. Objective At the end of this lesson, students should be able to write simple C++ programs using the standard I/O library, the String class, and primitive data types.

4. Review: A Simple C# Program using System; class Program { // a constant const int SIZE = 5; static void Main( ) { // a local variable double average =32.5; // arithmetic double newValue = average * SIZE; Console.WriteLine("The average value is {0}", average); Console.ReadLine(); }

5. Let’s Convert it to C++ using System; class Program { // a constant const int SIZE = 5; static void Main( ) { // a local variable double average =32.5; // arithmetic double newValue = average * SIZE; Console.WriteLine("The average value is {0}", average); Console.ReadLine(); }

6. Let’s Convert it to C++ using System; class Program { // a constant const int SIZE = 5; static void Main( ) { // a local variable double average =32.5; // arithmetic double newValue = average * SIZE; Console.WriteLine("The average value is {0}", average); Console.ReadLine(); } C++ is not a pure object oriented language, so all code does not need to be enclosed inside of a class.

7. Let’s Convert it to C++ using System; // a constant const int SIZE = 5; static void Main( ) { // a local variable double average =32.5; // arithmetic double newValue = average * SIZE; Console.WriteLine("The average value is {0}", average); Console.ReadLine(); } Main does not have to be static, in C++ it normally returns an int, and it is all lower case void main( ) //or void main(void) return;

8. Let’s Convert it to C++ using System; // a constant const int SIZE = 5; void main(void) //or int main(void) { // a local variable double average =32.5; // arithmetic double newValue = average * SIZE; Console.WriteLine("The average value is {0}", average); Console.ReadLine(); return; //or return 0; } The syntax of basic declarations, arithmetic, and control statements are the same as in C#

9. Let’s Convert it to C++ using System; // a constant const int SIZE = 5; int main( ) { // a local variable double average =32.5; // arithmetic double newValue = average * SIZE; Console.WriteLine("The average value is {0}", average); Console.ReadLine(); return 0; } C++ I/O is much different from C# (we’ll discuss the details later) cout << “The average value is “ << average << endl;

10. Let’s Convert it to C++ using System; // a constant const int SIZE = 5; int main( ) { // a local variable double average =32.5; // arithmetic double newValue = average * SIZE; Console.ReadLine(); return 0; } To keep the console window open, we’ll use a system call cout << “The average value is “ << average << endl; system(“PAUSE”);

11. Let’s Convert it to C++ using System; // a constant const int SIZE = 5; int main( ) { // a local variable double average =32.5; // arithmetic double newValue = average * SIZE; system(“PAUSE”); return 0; } Namespaces are declared differently in C++. Everything we will use is in the standard (std) namespace. cout << “The average value is “ << average << endl; using namespace std;

12. Let’s Convert it to C++ using namespace std; // a constant const int SIZE = 5; int main( ) { // a local variable double average =32.5; // arithmetic double newValue = average * SIZE; system(“PAUSE”); return 0; } Finally, we need to add a new pre-processor directive, that includes header files that are required for our program to compile correctly. The iostream header file is required when doing console I/O. cout << “The average value is “ << average << endl; #include

13. Here’s the Final C++ Program using namespace std; // a constant const int SIZE = 5; int main( ) { // a local variable double average =32.5; // arithmetic double newValue = average * SIZE; system(“PAUSE”); return 0; } cout << “The average value is “ << average << endl; #include

14. A Good C++ Code Skeleton using namespace std; // declare global constants here #include “skel.h” void main(void) { // declare local variable variables here // C++ statements system(“PAUSE”); } #include.h file.cpp file

15. Primitive Data Types C++ has fewer primitive data types than does C#, but the primary ones that we will use are exactly the same … int, double, bool, and char and unsigned. There is a major difference between C++ data types and C# data types. In C++, the size of a data type is determined by the underlying hardware, it is not defined by the language.

16. Assignment and Arithmetic work just as they do in C#.

17. C++ Input and Output In place of C#s Console class, we need two C++ Objects to do console input and output

18. cin cin is an object of the istream class. To use cin, you must #include iostream in your program. This object represents the standard input stream. The cin object is created automatically for you. keyboard buffer cin program keyboard buffer

19. coutis an object of the ostream class. This object represents the standard output stream. It is also created automatically for you. output buffer cout program cout display buffer

20. The Stream Insertion Operator, << a binary operator (it takes two operands) the left hand operand must be an output stream the right hand operand –is converted into text –the text data is then copied into the stream

21. display buffer int a = 5; a 0000 0000 0000 0101 the integer 5 0000 0000 0011 0101 the character 5 cout cout << a; 5

22. multiple pieces of data are output by cascading the << operator … cout << “The answer is “ << a;

23. If you want data to appear on a new line, you must explicitly add the newline character to the output stream. There is no WriteLine operation. Special characters are added to the stream using the escape character \ \t \n etc … cout << “The answer is “ << a << ‘\n’;

24. the endl stream manipulator can be added to the output stream. It does two things: It adds a new line to the stream. It forces the buffer to be output cout << “Hello” << endl;

25. Formatting Numbers Output formatting in C++ is quite different from C#’s output formatting.

26. To display a double or a float in standard decimal notation cout.setf(ios::fixed); setf( ) is a function in the cout object. It is responsible for setting formatting flags. We will study these in much more detail in a later section. In this case, we are setting the ios::fixed flag. This makes the output appear as a normal decimal number instead of in scientific notation. cout.setf(ios::showpoint); the ios::showpoint flag guarantees that a decimal point will be displayed in the output. cout.precision(2); the cout.precision( ) function determines how many digits will be displayed after the decimal point. The default formatting, is the “general” format. In this case precision defines the number of digits in total to be displayed

27. Example double price = 78.5; cout.setf(ios::fixed); cout.setf(ios::showpoint); cout.precison(2); cout << “The price is $” << price << endl;

28. The stream extraction operator, >> Also a binary operator The left operand must be an input stream Any initial white space is skipped, then the stream is read up to the next white space character ( tab, space, new-line ) If necessary, the text just read is converted to match the type of the right operand. An error occurs if the conversion cannot be done. The data is stored in the right operand

29. keyboard buffer cin int a; cin >> a; a 0000 0000 0011 0101 the character 5 0000 0000 0000 0101 5 72 hello reading stops when white space is encountered

30. In C#, we always read a string from the Console, and then used a Parse method to convert the string to the desired data type. In C++, this conversion happens via the >> operator. However, no exception occurs if the conversion cannot be done.

31. Failed Input Consider the following: A program contains the statements int number = 0; cin >> number What happens if the user types the letter “t”?

32. The stream extraction operator is not able to convert the letter “t” into a proper integer value. Three important things happen, without warning: 1.No input occurs, so the variable number contains whatever value it had previously. 2. The letter “t” remains in the input buffer, so a subsequent read operation will try to read it by error. 3. The object cin sets itself to a “failed” state, and subsequent input operations will all fail.

33. Handling Failed Input As noted, if input fails, no data is input. We can detect when this happens by testing the state of the input stream object. if (cin.fail( ) ) { cout << “Invalid input occured”;... }

34. There is a well known idiom in C++ that makes handling failed input much easier. The expression cin >> number; has a value, which is the value of the object cin itself. if the value of cin is “good”, we can go ahead and process the data. The statement to do this looks like if (cin >> number) { // process the input }

35. Recall that once the stream object fails, all subsequent read operations will fail. How do we fix that? The stream objects have a member function named clear( ), that resets the failed state back to good. cin.clear( );

36. Using the Stream State to Control a Loop cout << “\nEnter an integer value (or ‘q’ to quit): “; while (cin >> number) { // process the data } cin.clear( ); // clear the fail state string dummyValue; // get the ‘q’ out of the buffer cin >> dummyValue;... This code will process user input until a non-integer value is typed:

37. you can also cascade the stream extraction operator : cin >> a >> b;

38. You can control the size of an input field with the setw( n ) stream manipulator. cin >> setw(5) >> title; But … keep in mind that this can leave data in the buffer.

39. cin.get The get function of the istream class works similar to the stream extraction operator. With no parameter, it gets one character from the input stream. cin.get( );

40. cin.ignore( ) This function reads in a character and ignores it. The character read in is discarded. cin.ignore( );

41. cin.ignore( ) This version of the function reads in n characters and ignores them. cin.ignore(n); This version of the function reads in n characters or until it encounters the delimiter character, and ignores the characters read. cin.ignore(n, ‘\n’);

42. In C++, you can use the same style of cast as you did in C#, but the preferred way to cast in C++ is to write, for example Casting int number = static_cast myDoubleValue; just use int number = (int)myDoubleValue;

43. Strings C++ has a string class similar to C#’s string class, but not quite as powerful.

44. Declaring a String (you must #include ) string myName; string myName = Prof. Fairclough”;

45. Reading a line into a string This function is similar to cin.get( )except that it reads an entire line of data, including spaces, and the data is stored in a string object. This is the preferred way of reading in a line of data. It is equivalent to C#’s ReadLine method. getline(cin, stringName);

46. cin.ignore( ) … again Why is ignore useful? Try the following code… int numItems; string description; cout << “\nenter the number of items and description: “; cin >> numItems; getline(cin, description); When prompted, enter the data on two lines.

47. C++ Control Flow With a few minor exceptions, the statements that control flow through a C++ program look and work the same as they do in C#

48. Switch In C#, each case must contain a break statement. It is legal to drop through from one case to the next. You can switch on intergal and char types only. NOT strings! DARN!

49. switch (num) { case 1: a = a + 5; b = b + 3; case 2: a = a + 6; b = b + 4; case 3: a = a – 7; b = b – 1; } if num = 3, only this code executes if num = 2, then this code executes if num =1, then this code executes This is valid code in C++

50. There is no foreach statement in C++