Introduction to C++

1. Introduction to C++

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. Introduction In CS1410 we will study the C++ programming language. We do this for a number of reasons (1) We want our students to know at least 2 languages (2) C++ exposes some important ideas, like pointers, that are hidden from the programmer in other languages (3) Seeing the basic principles of programming used in a 2nd language will significantly increase you programming skills

5. Starting Point We will start out assuming that you know C# because that is what we teach in CS 1400. If you learned another language in your CS 1400 class, don’t worry. You’ll catch on.

6. 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(); } }

7. 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(); } }

8. 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.

9. 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 spelled main No capital M). int main( ) return 0;

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.WriteLine("The average value is {0}", average); Console.ReadLine(); return 0; } The syntax of basic declarations, arithmetic, and control statements are the same as in C#

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; 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;

12. 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”);

13. 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; } using namespace std; Namespaces are declared differently in C++. Everything we will use is in the standard (std) namespace. cout << “The average value is “ << average << endl;

14. Let’s Convert it to C++ #include <iostream> 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. 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;

15. Here’s the Final C++ Program #include <iostream> 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;

16. A Good C++ Code Skeleton #include <iostream> using namespace std; // declare global constants here int main( ) { // declare local variable variables here // C++ statements system(“PAUSE”); return 0; }

17. 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. 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.

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

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

20. cin cinis an object of the istreamclass. 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 keyboard buffer program cin

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

22. 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

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

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

25. If you want data to appear on a new line, you must explicitly add the newline character to the output stream. There is noWriteLine operation. Special characters are added to the stream using the escape character \ \t \n etc … cout << “The answer is “ << a << ‘\n’;

26. the endlstream 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;

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

28. To display a double or a float in standard decimal notation The default formatting, is the “general” format. In this case precision defines the number of digits in total to be displayed cout.setf(ios::fixed); cout.setf(ios::showpoint); cout.precision(2); 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. the ios::showpoint flag guarantees that a decimal point will be displayed in the output. the cout.precision( ) function determines how many digits will be displayed after the decimal point.

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

30. 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

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

32. 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 automatically. However, no exception occurs if the conversion cannot be done.

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

34. The stream extraction operator is not able to convert the letter “t” into a proper integer value. Three important things happen, without warning: 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 again. 3. The object cin sets itself to a “failed” state, and subsequent input operations will all fail.

35. 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”; . . . }

36. 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 cinobject 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 }

37. 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( );

38. Using the Stream State to Control a Loop This code will process user input until a non-integer value is typed: 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; . . .

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

40. 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.

41. 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( );

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

43. 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’);

44. Casting 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 int number = static_cast<int> (myDoubleValue);

45. Strings C++ has a string class what is similar to C#’s string class.

46. Declaring a String (you must #include <string>) string myName; string myName = “Prof. deBry”;

47. 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);

48. Additional Notes on the String Class Use + to concatenate two strings Use the member function size( ) to get the length of a string The [ ] operator can be used to access or modify individual characters of a string. No bounds checking is performed. The c_str( ) member function returns a char* based string.

49. The C11 Numeric Conversion Functions The C++11 standard contains new functions to convert the contents of a string into a numeric value. These are similar to C#’s Parse methods. stoi – converts a string to an int stod– converts a string to a double + 6 more for the other C++ numeric data types

50. The C11 Numeric Conversion Functions These functions attempt to convert the first part of a string into a numeric value. If a conversion cannot be performed, an invalid_argument exception is thrown.