1. Lecture 9m: Top-Down Design with Functions COS120 Software Development Using C++ AUBG, COS dept

2. 2 Exercise 8.1 Define a function and Build a program: to compute the area of a circle double FindArea(double rad);

3. 3 Exercise 8.2 Define a function and Build a program: to compute the circumference of a circle double FindCircum(double rad);

4. 4 Exercise 8.3 Define a function and Build a program: to compute the area of a square int FindSqArea(int side);

5. 5 Exercise 8.4 Define a function and Build a program: to compute the perimeter of a square int FindSqPerim(int side);

6. 6 Exercise 8.5 Define a function and Build a program: to solve the Miles-to-Kilometers conversion problem double ConvMilesToKms(double kms);

7. 7 Library functions List of some Mathematical Library Functions (#include, data type double): Function Purpose (return value) sqrt(x)Square root (x>=0) sin(x)Sine of angle x (in radians) pow(x,y)x y (power operator) cos(x)Cosine of angle x (in radians) exp(x)e x (e=2.71828…) tan(x)Tangent of angle x (in radians) log(x)Natural logarithm (x>0) ceil(x)Smallest integral not < than x log10(x)Base-10 logarithm (x>0) floor(x)Largest integral not > than x

8. 8 Library functions List of some Character Library Functions (#include ) Function Purpose (return value) char tolower(char c) Returns lowercase letter if c is uppercase. Otherwise, returns c. char toupper(char c) Returns uppercase letter if c is lowercase. Otherwise, returns c. bool isalpha(char c) Returns true if c is a letter (‘a’ … ‘Z’), otherwise false. bool isalnum(char c) Returns true if c is a letter or a digit, otherwise false. bool isdigit(char c) Returns true if c is a digit (‘0’ … ‘9’), otherwise false. bool isxdigit(char c) Returns true if c is a hex digit (‘0’…’9’, ‘a’… ‘f’, ‘A’…’F’). bool isspace(char c) Returns true if c is a space or tab(‘\t’) or new line (‘\n’).

9. 9 Before lecture end Lecture: Top-Down Design using Functions More to read: Friedman/Koffman, Chapter 03

10. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Chapter 3: Top-Down Design with Functions and Classes Problem Solving, Abstraction, and Design using C++ 5e by Frank L. Friedman and Elliot B. Koffman

11. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 11 Functions with Input Arguments Functions used like building blocks Build systems one function at a time –E.g. stereo components Use function arguments to carry information into function subprogram (input arguments) or to return multiple results (output arguments)

12. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 12 Functions with Input Arguments Arguments make functions versatile E.g.: rimArea = findArea(edgeRadius) - findArea(holeRadius);

13. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 13 void Functions with Input Arguments Give data to function to use Don’t expect function to return any result(s) Call format: fname (actual-argument-list); E.g.: drawCircleChar(‘*’);

14. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 14 drawCircleChar(‘*’); void drawCircle(char symbol) { cout << “ “ << symbol << endl; cout << “ “ << symbol << “ “ << symbol << endl; } // end drawCircle ‘*’ symbol

15. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 15 Functions with Arguments and a Single Result Functions that return a result must have a return statement: Form:return expression; Example:return x * y;

16. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 16 #include using namespace std; const float PI = 3.14159; float findCircum(float); float findArea(float); int main( ) { float radius = 10.0; float circum; float area; circum = findCircum(radius); area = findArea(radius); cout << “Area is “ << area << endl; cout << “Circumference is “ << circum << endl; return 0; }

17. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 17 // Computes the circumference of a circle with radius r // Pre: r is defined and is > 0. // PI is a constant. // Post: returns circumference float findCircum(float r) { return (2.0 * PI * r); } // Computes the area of a circle with radius r // Pre: r is defined and is > 0. // PI is a constant. // Post: returns area float findArea(float r) { return (PI * pow(r,2)); } Figure 3.12 Functions findCircum and findArea

18. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 18 circum = findCircum(radius); float findCircum(float r) { return (2.0 * PI * r); } 10 radius 10 r 62.8318 call findCircum 62.8318 circum

19. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 19 Function Definition (Input Arguments with One Result) Syntax: // function interface comment ftype fname(formal-parameter-declaration-list) { local variable declarations executable statements }

20. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 20 Function Definition (Input Arguments with One Result) Example: // Finds the cube of its argument. // Pre: n is defined. int cube(int n) { return (n * n * n); }

21. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 21 Function Prototype (With Parameters) Form: ftype fname(formal-parameter-type-list); Example: int cube(int);

22. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 22 Function Interface Comments Preconditions –conditions that should be true before function is called –// Pre: r is defined Postconditions –conditions that will be true when function completes execution –// Post: Returns circumference

23. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 23 Problem Inputs vs. Input Parameters Problem inputs –variables that receive data from program user –through execution of input statement Input parameters –receive data through execution of function call statement –must be defined before function is called

24. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 24 Listing 3.14: Testing function testScale.cpp // File testScale.cpp // Tests function scale. #include using namespace std; // Function prototype float scale(float, int);

25. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 25 int main() { 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; } Listing 3.14: Testing function testScale.cpp (continued)

26. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 26 // Multiplies its first argument by the power of 10 // specified by its second argument. // Pre: x and n are defined and library cmath is // included float scale(float x, int n) { float scaleFactor; // local variable scaleFactor = pow(10, n); return (x * scaleFactor); } Listing 3.14: Testing function testScale.cpp (continued)

27. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 27 float scale(float x, int n) { float scaleFactor; // local variable scaleFactor = pow(10, n); return (x * scaleFactor); } cout << "Result of call to function scale is " << scale(num1, num2) << endl;...... Formal parameters Information flow Actual arguments Listing 3.14: Testing function testScale.cpp (continued)

28. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 28 Argument/Parameter List Correspondence Must have same number of actual arguments and formal parameters Order of arguments in the lists determines correspondence Each actual argument must be of a data type that is compatible to the corresponding formal parameter The names of the actual arguments do not need to correspond to the formal parameters

29. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 29 Function Data Area Each time function is executed –an area of memory is allocated for storage of the function’s data (formal parameters and local variables) –it is created empty with each call to the function When the function terminates –the data area is lost

30. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 30 Data Areas After Call scale(num1, num2); Function main Data Area Function Scale Data Area num1 num2 x n scaleFac tor 2.5 -2 2.5 -2 ?

31. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 31 Testing Functions Using Drivers Any function can be tested independently Test driver –defines values for the function’s arguments –calls the function –displays the value returned for verification

32. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 32 Scope of Names Scope - where a particular meaning of a name is visible or can be referenced Local - can be referred to only within the one function –applies to formal argument names constants and variables declared within the function Global - can be referred to within all functions –useful for constants –must be used with care

33. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 33 Listing 3.15 Outline of program for studying scope of names

34. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 34 3.2 Library Functions Goals of software engineering –reliable code –accomplished by code reuse C++ promotes code reuse with predefined classes and functions in the standard library

35. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 35 C++ cmath Library Typical mathematical functions e.g. sqrt, sin, cos, log Function use in an assignment statement y = sqrt(x); Function name Function argument Function call

36. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 36 Example: sqrt Function Square root function Function sqrt as a “black box” X is 16.0Result is 4.0

37. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 37 Listing 3.5 Illustration of the use of the C++ sqrt function

38. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 38 Listing 3.5 Illustration of the use of the C++ sqrt function (continued)

39. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 39 Table 3.1 Some Mathematical Library Functions

40. Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 40 Table 3.1 Some Mathematical Library Functions (continued)

41. 41 Thank You For Your Attention!