Chapter 8

1. Chapter 8 Introduction to High-Level Language Programming

2. Objectives In this chapter, you will learn about • Where do we stand? • High-level languages • Introduction to C++ • Virtual data storage • Statement types • Putting the pieces together

3. Objectives Postponed(Covered in CS23021) • Functions • Managing complexity • Object-oriented programming • Graphical programming • The big picture: Software engineering

4. Where Do We Stand? • Early days of computing • Programmers used assembly language • Programs written by technically oriented people • Assembler programs • Were machine specific • Required programmers take a microscopic view of a task • Later decades • Programmers demanded a more comfortable programming environment • Programs could be written by “nontechie” people • Programs could be portable rather than machine specific • Programmers could avoid data storage and movement issues

5. High-level Languages • High-level programming languages • Called third-generation languages • Machine language was “first generation” • Assembly language was “second generation” • Overcame deficiencies of assembly language • Programmer didn’t need to manage details of data storage or movement

6. High-level Languages (continued) • Expectations of a high-level language program (continued) • Programmer can take a macroscopic view of tasks; “primitive operations” can be larger • Program will be portable • Code will be closer to standard English and use standard mathematical notation

7. Figure 8.1 Transitions of a High-level Language Program

8. Introduction to C++ • Some components of program on next slide • Comments • Anything following “//” on a line is a comment • Give information to human readers of code • The “include” directive • The linker includes object code from a library • C++ does not provide input or output of data (I/O) • The “using” directive • Tells compiler to look in a namespace for definitions not mentioned in the program • Used here for I/O commands “cin” & “cout” • Main program code in brackets after “main”

9. A Simple C++ Program Figure 8.2

10. Figure 8.3 The Overall Form of a Typical C++ Program

11. Data Types • Identifiers: Names in a programming language • Any combination of letters, digits, and underscore symbol that does not start with a digit. • Should select names suggestive of meaning • Keywords: Have special meanings in C++ • Also called reserved words. • Can not be used as an identifier • C++ is a case-sensitive, free-format language • Data items can be constants or variables

12. Data Types (continued) • A declaration of a data item tells • Whether the item is a constant or a variable • The identifier used to name the item • The data type of the item

13. Figure 8.5 Some of the C++ Standard Data Types

14. Data Types (continued) • An array • Groups together a collection of memory locations, all storing data of the same type • Example Int Hits[12] Figure 8.6 A 12-Element Array Hits

15. Statement Types • Input/output statements • Input statement • Collects a specific value from the user for a variable within the program • Output statement • Writes a message or the value of a program variable to the user’s screen or to a file

16. Statement Types (continued) • Assignment statement • Assigns a value to a program variable • Control statement • Directs the flow of control • Can cause it to deviate from usual sequential flow

17. Input/Output Statements • Example • Pseudocode Get value for Radius (interactively from keyboard) • C++ cin >> Radius; • cin: Input stream • Code for extraction operator (>>) and the definition of the cin stream come from the iostream library and std namespace

18. Input/Output Statements (continued) • Example • Pseudocode Print the value of Circumference (on screen) • C++ cout << Circumference; • cout: Output stream • Code for the insertion operator (<<) and the definition of the cout stream come from the iostream library and std namespace

19. Input/Output (cont.) • Consider real numbers such as 84.8232 • The fixed format output of this number would be 84.8232 • In scientific notation, this output would be 8.48232e+001 • The computer is free to choose the output style. • To specify fixed format output, include the following formatting statement in the program cout.setf(ios::fixed); • To require the output be in scientific notation, use cout.setf(ios::scientific); • To require two decimal places, use cout.precision(2)

20. Output using literal strings • Suppose we want to output message before the value, such as The circumference that corresponds to this radius is 84.8234 • This could be accomplished using cout << “The concumference that corresponds “ << “to this radius is “ << Circumference • Many other output features are available • Some additional information is given in textbook • We won’t cover the output options in detail here.

21. The Assignment Statement • General form • Pseudocode Set the value of “variable” to “arithmetic expression” • C++ assignment statement evaluation variable = expression; • Expression on the right is evaluated • The result is written into the memory location specified on the left • Example: Consider assemby code for A= B + C - 3;

22. Assignment Statements (cont.) • The C++ symbols for four basic operations + Addition - Subtraction * Multiplication / Division • Example: The product of A & B is A*B. • Data Type Considerations: • If A and B are integers, then A/B is the integer obtained by truncation: 7/2 is 3 • If either A or B is a real number then A/B is a real number: 7/2 is 3.5 • Other data-type considerations are covered in textbook, and will be used, as needed.

23. Control Statements • Types of control mechanisms • Sequential • Instructions are executed in order • Conditional • Choice of which instructions to execute next depends on some condition • Looping • Group of instructions may be executed many times

24. Control Statements (continued) • Sequential is the default mode of execution • Conditional flow of control • Evaluation of a Boolean condition (also called a Boolean expression) • Which programming statement to execute next is based on the value of the Boolean condition (true or false)

25. Control Statements (continued) • Conditional flow of control (continued) • if-else statement if (Boolean condition) S1; else S2; • if variation of the if-else statement if (Boolean condition) S1;

26. Figure 8.10 Conditional Flow of Control (flowchart) (If-Else)

27. Figure 8.11 If-Else with Empty Else

28. Control Statements (continued) • Looping (iteration) • The loop body may be executed repeatedly based on the value of the Boolean condition • while statement while (Boolean condition) S1;

29. Figure 8.12 While Loop

30. Putting the Pieces Together • At this point, we can • Perform input and output • Assign values to variables • Direct the flow of control using conditional statements or looping • For a complete program, we need to • Assemble the statements in the correct order • Fill in the missing pieces

31. Meeting Expectations • C++ meets the four expectations for a high-level programming language • Expectations • A programmer need not manage the details of the movement of data items within memory, nor pay any attention to where they are stored

32. Meeting Expectations • Expectations (continued) • Programmer can take a macroscopic view of tasks, thinking at a higher level of problem solving • Programs written in high-level languages will be portable rather than machine-specific • Programming statements in a high-level language • Will be closer to standard English • Will use standard mathematical notation

33. Pseudocode Language Instructions in C++(Sections 8.1 – 8.6) Recall pseudocode language instructions(pg 58) • Computation: • Set value of “variable” to “arithemetic expression” • Input/Output: • Get a value for “variable” • Print the value for “variable” • Print the message “message” • Conditional: • If “a boolean expression” is true then First set of algorithmic operations Else Second set of algorithmic operations

34. Pseudocode Language Instructions(cont.) • Iteration (looping): • While (a boolean condition is true) do operation operation ..... operation End of Loop

35. Computation: Expressions in C++ An expression in C++ is a sequence of operators and operands which adhere to the C++ syntax rules. The operators are grouped according to an order of precedence, and associativity

36. Computation: Expressions in C++ Assume b = 5, c = 3, d = 4, e = 2 Example 1: a = b + c * d; Example 2: a = b + c * d – e; Example 3: a = (b + c) * (d-e); Example 4: a = b / c; Example 5: a = b % c; Example 6: a = b = c – d; Other: +=, -=, *= , /=, %= ???

37. Computation (cont.) • Consider equation: ax2 + bx + c = 0 • The roots are x = ( –b  sqrt(b2 – 4ac) ) / 2a • Using a high level language we could write: • discrim = b*b – 4*a*c; • root1 = (-b + sqrt(discrim)) / (2*a); • root2 = (-b – sqrt(discrim)) / (2*a); • This closely resembles the way we look at the problemmathematically

38. Input and Output in C++ /* circle03.cpp Gets the radius of a circle, calculatesit’s circumference and prints out the result */ #include <iostream> using std::cin; using std::cout; int main() { const double PI = 3.14159; double radius = 0.0, circumference = 0.0; cout << "Please enter the radius " << '\n'; cin >> radius; circumference = 2 * PI * radius; cout << “The circumference is: “ ; cout << circumference << “.\n”; return 0; } i/o example #3 • cout – prompt user for data • << (insertion operator) • cin – store data in a variable • >> (extraction operator) • cout – output data entered

39. Conditional Statements in C++ • Conditional flow of control (continued) • if-else statement if (Boolean condition) S1; else S2; • if variation of the if-else statement if (Boolean condition) S1;

40. Figure 8.12 Conditional Flow of Control (If-Else)

41. Figure 8.13 If-Else with Empty Else

42. Iterative Statement in C++ • Looping (iteration) • The loop body may be executed repeatedly based on the value of the Boolean condition • while statement while (Boolean condition) S1;

43. Figure 8.14 While Loop

44. Interative Example in C++ Sum = 0; //initialize Sum cout << “Please enter the numbers to add; “; cout << “terminate with a negative number.” << endl; cin >> Number; // this will get the first value while (Number >= 0) { Sum = Sum + Number; cin >> Number; } cout << “The total is “ << Sum << endl;

45. Summary • In a high-level language, the programmer: • Need not manage storage • Can think about the problem at a higher level • Can use more powerful and more natural-language-like program instructions • Can write a much more portable program