Circle Area/Circumference Calculator

1. Chapter 3 Top-Down Design with Functions Dr. J.-Y. Pan Dept. Comm. Eng. Nat. Chung Cheng Univ. http://ant.comm.ccu.edu.tw jypan@comm.ccu.edu.tw

2. Outline • Building a program • CaseStudyFinding Area/Circumference of a circle • Top-Down Design and Structure Charts • Case Study: Drawing Simple Diagrams • Code reuse and functions

3. Building Programs from Existing Information(Design  Implementation) • Programs = Data structures + Algorithms • How to implement a program? You can… • editing data requirements conform to C syntax for constant macro and variable declarations (Data structures) • use the initial algorithm and refinements as program comments, and then write C statements for them(Algorithms)

4. CaseStudyFinding the Area and Circumference of a circle(1/4) Step 1: Problem • Get the radius of a circle. Compute and display the circle’s area and circumference.

5. CaseStudyFinding the Area and Circumference of a circle(2/4) Step 2: Analysis • Problem Constant • PI 3.14159 • Problem Inputs • radius • Problem Outputs • area • circum • Relevant Formulas • Area of a circle = π x radius2 • Circumference of a circle = 2 π x radius

6. CaseStudyFinding the Area and Circumference of a circle(3/4) Step 3: Design • Initial Algorithm 1. Get the circle radius 2. Calculate the area 3. Calculate the circumference 4. Display the area and the circumference • Algorithm Refinement 2.1 Assign PI * radius * radius to area 3.1 Assign 2 * PI * radius to circum

7. CaseStudyFinding the Area and Circumference of a circle(4/4) Step 4: Implementation (Figure 3.2、Figure 3.3) Step 5: Testing

8. Outline of Program calculating Circle

9. Calculating Area and Circumference of a Circle

10. Top-Down Design and Structure Charts • When a problem is more complex than those we have seen so far… • Must break up the problem into subproblems to develop the program solution, and so on… • Top-down design • A small problem is easier to solve • A picture is worth a thousand words • Structure chart • a documentation tool that shows the relationship among the subproblems of a problem

11. Case Study: Drawing Simple Diagrams(1/2) Step 1: Problem • You want to draw some simple diagrams on your printer or screen. For example, a female stick figure in Fig.3.9. Step 2: Analysis • three basic components • a circle • a base line • Intersecting lines

12. Case Study: Drawing Simple Diagrams(2/2) Step 3: Design (Figure 3.10) • Initial algorithm • 1. Draw a circle. • 2. Draw a triangle. • 3. Draw intersecting lines. • Refinements • 2.1 Draw intersecting lines. • 2.2 Draw a base.

13. Figure 3.10 Structure Chart for Drawing a Stick Figure

14. Figure 3.11 Function Prototypes and Main Function for Stick Figure

15. Figure 3.12 Function draw_circle

16. Figure 3.13 Function draw_triangle

17. Figure 3.14 Whole Program to Draw a Stick Figure

18. Figure 3.14 Program to Draw a Stick Figure (cont’d)

19. Execution order of subprograms and main Figure 3.15 Flow of Control Between the main Function and a Function Subprogram 2. Allocate memory for variables declared 1. When executes function call statement, it transfer control to referenced function. 3. Execute statements in subprogram function 6. Execute next statement in the main function 4. Return control to the main function 5. Release memory

20. Code reuse and functions • Why reinvent the wheel? • C provides predefined functions • Standard library • Appendix B shows ANSI C standard libraries • P.800~801, stdio.h所列之functions • P.799, math.h所列之functions • P.802, string.h所列之functions (教到字串時請自學) • 自行參考其功用，大略記一下 function call y = sqrt(x); Function sqrt as a “Black Box” function name argument

21. Advantages of Using Function Subprograms • Easier to apportion(分配) programming tasks in a team • Procedure abstraction • a programming technique in which a main function consists of a sequence of function calls and each function is implemented separately • Defer implementation details (How to do) from a subproblem (What to do). • Focusing on one function at a time is much easier • Reuse of function subprograms • Functions can be executed more than once • Functions can be used in other programs or functions

22. Lego blocks “protrusions” and “cups” Input arguments Arguments used to pass information into a function subprogram Output arguments Arguments used to return results to the calling function Functions with Input/output Arguments

23. Actual argument • an expression used inside the parentheses of a function call • Formal parameter • an identifier that represents a corresponding actual argument in a function definition TestingFunctionscale

24. Argument List Correspondence(The not rules) • The number of actual arguments used in a call to a function must be the same as the number of formal parameters listed in the function prototype. • The order of arguments in the lists determines correspondence. • Each actual argument must be of a data type that can be assigned to the corresponding formal parameter.

25. The Function Data Area • When a function call is executed… • a memory area is allocated for storage of function data (ex. formal parameter, local var) • When function terminates… • function data area is always lost • Again? • Local variable • initially undefined (usually…)

26. Data Areas After Call scale(num_1, num_2);

27. Question? • A good question deserve a good grade…