1. Top-Down Design with Functions and Classes Chapter 3

2. 2 3.1 Building Programs from Existing Information –Reuse of existing programs –Develop program in stages –Compile along the way –Keep it small –Comments to describe actions

3. 3 Washers.cpp // File: washers.cpp // Computes the weight of a batch of flat // washers. #include using namespace std; int main() { const float PI = 3.14159; float holeDiameter; // input -

4. 4 Washers.cpp float edgeDiameter; // input - diameter float thickness; // input - thickness float density; // input - density float quantity; // input - number float weight; // output - weight float holeRadius; // radius of hole float edgeRadius; // radius of outer edge float rimArea; // area of rim float unitWeight; // weight of 1 washer

5. 5 Washers.cpp cout << "Inner diameter in centimeters: "; cin >> holeDiameter; cout << "Outer diameter in centimeters: "; cin >> edgeDiameter; cout << "Thickness in centimeters: "; cin >> thickness; cout << "Material density in grams per cubic centimeter: "; cin >> density; cout << "Quantity in batch: "; cin >> quantity;

6. 6 Washers.cpp // Compute the rim area. holeRadius = holeDiameter / 2.0; edgeRadius = edgeDiameter / 2.0; rimArea = PI * edgeRadius * edgeRadius - PI * holeRadius * holeRadius; // Compute the weight of a flat washer. unitWeight = rimArea * thickness * density; // Compute the weigh weight = unitWeight * quantity;

7. 7 Washers.cpp // Display the weight cout << "The expected weight of the batch is " << weight; cout << " grams." << endl; return 0; }

8. 8 Washers.cpp Program Output Inner Diameter in centimeters: 1.2 Outer Diameter in centimeters: 2.4 Thickness in centimeters: 0.1 Material density in grams per cubic centimeter: 7.87 Quantity in batch: 1000 The expected weight of the batch is 2670.23 grams

9. 9 3.2 Library Functions –Goal of Structured Programming Error free code –Reusability Don’t reinvent the wheel –C ++ provides collection of functions –Organized in Libraries Library examples Table 3.1

10. 10 C++ Math Library –Functions in the Math library sqrtcos sinpow Examples Table 3.1 –Function use in Assignments y = sqrt (x); sqrt is function name x is function argument –Activated by a “function call” –Result of execution is assigned to variable y

11. 11 C++ Math Library (cont) Function sqrt as a “black box” Square root computation X is 16.0Result is 4.0

12. 12 C++ Library Functions –We can effectively utilize existing functions by learning to read function prototypes with the preconditions and postconditions. –Example prototype (or signature) t double sqrt(double x) t // PRE: x >= 0.0 t // POST: Returns the square root of x.

13. 13 Preconditions and Postconditions –Comments that represents a contract between the implementor of a function and the user (client) of that function. –We'll look at two such comments: Precondition: What the function requires. Postcondition: What the function will do if the precondition is met.

14. 14 Preconditions and Postconditions –The preconditions are the circumstances that must be true before the function can successfully fulfill the promised postconditions. –Example (Precondition abbreviates to PRE: double sqrt(double x); // PRE: x >= 0 // POST: Returns square root of argument X

15. 15 SquareRoot.cpp // File: squareRoot.cpp // Performs three square root computations #include // sqrt function #include // i/o functions using namespace std; int main() { float first; float second; float answer;

16. 16 SquareRoot.cpp // Get first number and display its square root. cout << "Enter the first number: "; cin >> first; answer = sqrt(first); cout << "The square root of the first number is " << answer << endl; // Get second number and display its square root. cout << "Enter the second number: "; cin >> second; answer = sqrt(second); cout << "The square root of the second number is " << answer << endl;

17. 17 SquareRoot.cpp // Display the square root of the sum of first // and second. answer = sqrt(first + second); cout << "The square root of the sum of both numbers is " << answer << endl; return 0; }

18. 18 SquareRoot.cpp Program Output Enter the first number: 9 The square root of the first number is 3 Enter the second number: 16 The square root of the second number is 4 The square root of the sum of both numbers is 5

19. 19 3.3 Top-Down Design and Structure Charts Original Problem Detailed subproblem s Level 0 Level 1 Level 2

20. 20 3.4 Functions without Arguments –Functions used in Top-Down Design –main() is just a function called by OS –C++ program is a collection of Functions top level function is called the main() lower level functions –User Defined or Libraries –Example StkFigMn.cpp

21. 21 StickFigure.cpp // File: stickFigure.cpp // Draws a stick figure #include using namespace std; // Functions used... void drawCircle(); // Draws a circle void drawTriangle(); // Draws a triangle void drawIntersect(); // Draws intersecting lines void drawBase(); // Draws a horizontal line

22. 22 StickFigure.cpp int main() { // Draw a circle. drawCircle(); // Draw a triangle. drawTriangle(); // Draw intersecting lines. drawIntersect(); return 0; }

23. 23 Function Calls –We can call a function and get results without knowing the implementation of that function. pow(x, y) returns x to the yth power. –For now, we need not know exactly how a function is implemented. –However, we do need to know how to use the function.

24. 24 Function Calls –This general form of a function call: function-name ( optional argument-list ); –Example function call: drawCircle (); –The function name is drawCircle –No arguments to the function

25. 25 Function Prototype –This general form of a function prototype: type function-name ( optional argument-list ); –Example function prototype: void skipThree (); –Type int - float - char –Name –( ); –Descriptive comment

26. 26 Function Definition –General form of a function definition: type function-name ( optional argument-list ) { local-declarations- function body executable-statements } –Example function definition: void drawTriangle ()

27. 27 Function Definition void drawTriangle () { // Draw a triangle. drawIntersect (); drawBase (); } function header function body

28. 28 StickFigure.cpp // Draws a circle void drawCircle() { cout << " * " << endl; cout << " * *" << endl; } // end drawCircle

29. 29 StickFigure.cpp void drawCircleChar(char symbol) { cout << " " << symbol << " " << endl; cout << " " << symbol << " " << symbol << endl; cout << " " << symbol << " " << symbol << endl; } // Draws a triangle void drawTriangle() { drawIntersect(); drawBase(); }

30. 30 StickFigure.cpp // Draws intersecting lines void drawIntersect() { cout << " / \\ " << endl; } // draws a horizontal line void drawBase() { cout << " -------" << endl; }

31. 31 Order of Execution int main() { drawCircle(); drawTriangle(); drawIntersect(); return 0; } void drawCircle() { cout << “ * “ << endl; cout << “ * * “ << endl; }

32. 32 Function Advantages –Program team on large project –Simplify tasks –Each Function is a separate unit –Top-down approach –Procedural abstraction –Information hiding –Reuse (drawTriangle)

33. 33 Abstraction –Abstraction: Refers to the act of ignoring details to concentrate on essentials. Allows us to use complicated things with little effort (CD players, automobiles, computers ).

34. 34 Displaying User Instructions t We still have not covered passing in and out of a function t Following example shows displaying info –instruct(); function call in main

35. 35 Instruct.cpp // DISPLAYS INSTRUCTIONS TO THE USER // OF AREA/CIRCUMFERENCE PROGRAM int instruct () { cout << "This program computes the area and " << endl; cout << "circumference of a circle. " << endl << endl; cout << "To use this program, enter the radius of the " << endl; cout << "circle after the prompt" << endl;

36. 36 Instruct.cpp cout << "Enter the circle radius: " << endl << endl; cout << "The circumference will be computed in the same ” << endl; cout << "units of measurement as the radius. The area " << endl; cout << "will be computed in the same units squared." << endl << endl; }

37. 37 Program Output This program computes the area and circumference of a circle. To use this program, enter the radius of the circle after the prompt Enter the circle radius: The circumference will be computed in the same units of measurement as the radius. The area will be computed in the same units squared.

38. 38 3.5 Functions with Input Arguments –Functions used like building blocks –Build systems one functions at a time Stereo Components –Use function return values and arguments to communicate between functions –Discuss AreaMain.cpp Flow of arguments and returns

39. 39 Function Call Form:fname (actual arg list); Example:scale (3.0, z);

40. 40 Function Return t Functions must return a value unless declared as void Form:return expression; Example:return x * y;

41. 41 Function Definition Form: type fname (formal arg list) { function body } Example: float scale(float x, int n) { float scaleFactor; scaleFactor = pow(10, n); return (x * scaleFactor); }

42. 42 Function Prototype Form: type fname (formal arg type list); Example: float scale (float x, int n);

43. 43 TestScale.cpp // File testScale.cpp // Tests function scale. #include using namespace std; // Function prototype float scale(float, int); int main() {

44. 44 TestScale.cpp float num1; int num2; // Get values for num1 and num2 cout << "Enter a real number: "; cin >> num1; cout << "Enter an integer: "; cin >> num2; // Call scale and display result. cout << "Result of call to function scale is " << scale(num1, num2) << endl; return 0; }

45. 45 TestScale.cpp float scale(float x, int n) { float scaleFactor; scaleFactor = pow(10, n); return (x * scaleFactor); }

46. 46 Argument / Parameter List Correspondence –Functions can have more than 1 arg –Correspondence between Actual & Formal arguments Function call scale (3.0, z); Actual ArgumentFormal Argument 3.0x zn

47. 47 Argument / Parameter List Correspondence float scale(float x, int n) { float scaleFactor; scaleFactor = pow(10, n); return (x * scaleFactor); }

48. 48 Argument / Parameter List Correspondence Function call scale (x + 2.0, y); Actual ArgumentFormal Argument x + 2.0x y y

49. 49 Argument / Parameter List Correspondence Function call scale (y, x); Actual ArgumentFormal Argument yx xy Watch for type matches in formal and actual arguments

50. 50 Key Points Ê The substitution of the value of an actual argument in a function call for its corresponding formal argument is strictly positional. That is, the value of the first actual argument is substituted for the first formal argument; the second and so on

51. 51 Key Points Ë The names of these corresponding pairs of arguments are no consequence in the substitution process. The names may be different, or they may be the same. Ì The substituted value is used in place of the formal argument at each point where that argument appears in the called function.

52. 52 3.6 Scope of Names t Variable declared in a function has a local scope within the function t Same for variables declared in the main t Variable declared before main is global scope –Call anywhere in program t Functions declared globally

53. 53 Scope of Names t Positional correspondence t Type consistent is key because of positional correspondence –Argument types –Return types

54. 54 Scope of Names t Type of a value returned by a called function must be consistent with the type expected by the caller as identified in the prototype t Type of an actual argument in a function call must be consistent with the type of its corresponding formal argument

55. 55 3.7 Extending C++ through Classes –Discuss two classes String class part of compiler Money class is a user defined class –#include –#include “money.h”

56. 56 String Class t Declaring string objects t Reading & Displaying strings t Assignment & Concatenation t Operator Overloading t Dot Notation t Member Functions t Object Assignments

57. 57 Declaring string Objects t A number of ways to declare string firstName, lastName; string wholeName; string greeting = “Hello “;

58. 58 Reading & Displaying string Objects t Use extraction operator >> & the stream cin for input –cin >> firstName; t Use insertion operator << & the stream cout for output –cout << greeting << wholeName << endl;

59. 59 Reading & Displaying string Objects getline (cin, lastName, ‘\n’); reads all characters typed in from the keyboard up to the new line into the string object

60. 60 StringOperations.cpp // FILE: StringOperations.cpp // ILLUSTRATES STRING OPERATIONS #include using namespace std; int main () { string firstName, lastName; string wholeName; string greeting = "Hello "; cout << "Enter your first name: "; cin >> firstName;

61. 61 StringOperations.cpp cout << "Enter your last name: "; cin >> lastName; // Join names in whole name wholeName = firstName + " " + lastName; // Display results cout << greeting << wholeName << '!' << endl; cout << "You have " << (wholeName.length () - 1) << " letters in your name." << endl;

62. 62 StringOperations.cpp // Display initials cout << "Your initials are " << (firstName.at(0)) << (lastName.at(0)) << endl; return 0; }

63. 63 StringOperations.cpp Program output Enter your first name: Caryn Enter your last name: Jackson Hello Caryn Jackson! You have 12 letters in your name. Your initials are CJ

64. 64 Assignment t Stores the first and last name –wholeName = firstName + “ “ + lastName; t Concatenation –+ joins the two objects together t “ “ for string values not ‘ ‘

65. 65 Operator Overloading t + normally means addition but with strings it means concatenation t The + can take on many meanings –Operator Overloading –C++ can have multi meanings to 1 operator –>> & << are overloaded operators –* / - == = all can be overloaded

66. 66 Dot Notation t Dot notation used to call an objects member functions wholeName.length(); –Applies member function length to string object wholeName –Function returns the objects length –Table 3.3 lists some additional functions

67. 67 Money Class t Process money objects t Two attributes –dollars –cents t Why do this ?? Why not float ??

68. 68 Money Class t Allocate a money object –money creditLimit = 5000.00; t Assignments –taxAmount = salePrice * taxPercent/100.0; –finalCost = salePrice + taxAmount;

69. 69 MoneyDemo.cpp // FILE: MoneyDemo.cpp // ILLUSTRATES MONEY OPERATIONS #include #include "money.h" using namespace std; int main () { // Local declarations const float taxPercent = 6.25; money creditLimit = 5000.00;

70. 70 MoneyDemo.cpp money salePrice; money taxAmount; money finalCost; cout << "Enter item price: "; cin >> salePrice; // Compute tax amount taxAmount = salePrice * taxPercent / 100.0; // Compute final cost finalCost = salePrice + taxAmount;

71. 71 MoneyDemo.cpp // Display sales receipt cout << "Sales receipt" << endl; cout << "Price " << salePrice << endl; cout << "Tax " << taxAmount << endl; cout << "Paid " << finalCost << endl << endl; // Compute new credit limit cout << "Your initial credit limit is " << creditLimit << endl; creditLimit = creditLimit - finalCost; cout << "Your new credit limit is " << creditLimit << endl; return 0; }

72. 72 MoneyDemo.cpp Program output Enter item price: 345.77 Sales Receipt Price $345.77 Tax $21.61 Paid $367.38 Your initial credit limit is $5,000.00 Your new credit limit is $4,632.62

73. 73 Header and Implementation Files t Header file (.h) –File containing information that C++ needs to compile a program that accesses a user-defined class t Implementation file (.cpp) –File containing the C++ code for the operators of a user defined class

74. 74 3.8 Common Programming Errors –Semicolon in Function Prototype (Declaration) –Inconsistencies in Number of Arguments Too few arguments in a call Too many arguments in a call Incorrect number of arguments in call Extra argument in call –Argument Mismatch Correct position (formal & actual params)

75. 75 Common Programming Errors –Function Prototype & Definition Mismatches Both are the same except for the ; –Return Statements “Return value expected” “Function should return value” –Missing Object Name in Call to Member Function –Missing #include –Type Mismatches