1. Chapter 6 Modular Programming Dr. J.-Y. Pan Dept. Comm. Eng.
Nat. Chung Cheng Univ.

2. 本章重點
Pointer
Name scope
Testing skill

3. If a reference x is of type “whatever-type”, the reference &x is of type “pointer to whatever-type,” that is, “whatever-type *.”

4. Figure 6.5 Comparison of Direct and Indirect Reference

5. 6.1 (cont) Meaning of * Symbol
Three distinct meanings of the symbol *
Multiplication
3 * x + 4 (expression)
Part of the names of the parameters’ data types
pointer to
char *signp; (declaration)
Unary indirection operator
follow the pointer
*signp = ‘+’; (execution statement)

6. 6.1 Function With Output Parameter
Argument lists provide the communication links between the main function and its function subprograms.
Arguments enable a function to manipulate different data each time it is called.
When a function call executes, the computer allocates memory space in the function data area for each formal parameter. The value of each actual parameter is stored in the memory cell allocated to its corresponding formal parameter.

7. Figure 6.1 Function separate

8. Pointer
A memory cell whose content is
the address of another memory cell
Fig 1.4
Fig 3.15
Actual & Formal

9. 6.2 Multiple Calls to a Function with Input/Output Parameters
sort
A rearrangement of data in a particular sequence (increasing or decreasing)
Example 6.2
The main function in Fig. 6.6 gets three data values and rearranges the data in increasing sequence.

10. Figure 6.6 Program to Sort Three Numbers

11. Figure 6.6 Program to Sort Three Numbers (cont’d)
Comparing to p.164, Fig 4.5

12. 6.2 (cont) Trace of Program to Sort Three Numbers
Statement
num1
num2
num3
Effect
scanf(“...”, &num1, &num2, &num3);
7.5
9.6
5.5
Enter data
Order(&num1, &num2);
No change
Order(&num1, &num3);
Switch
Order(&num2, &num3);
printf(“...”, num1, num2, num3)
Display

13. Figure 6. 7 Data Areas After temp =
Figure 6.7 Data Areas After temp = *smp; During Call order(&num1, &num3);

14. Program Style
Functions that return a single value are the easiest functions for a program reader to deal with.
If a function subprogram has a meaningful name, the reader can often get a good idea of what is happening in the calling function.

15. 6.3 Scope of Names
The scope of a name refers to the region of a program where a particular meaning of a name is visible or can be referenced.
Name is defined as constant macros and their scope begins at their definition and continues to the end of the source file.

16. Figure 6.8 Outline of Program for Studying Scope of Names

17. Scope of Names Use in Fig. 6.8

18. 6.4 Formal Output Parameters as Actual Arguments
Fig. 6.9 shows a function that scans a data line representing a common fraction of the form
numerator / denominator
Numerator is an integer
Denominator is a positive integer
Figure 6.10 shows the data areas for scan_fraction and the function calling it.

19. Figure 6.9 Function scan_fraction
nump &slash denomp
Driver: Fig 6.15

20. Figure 6.10 Data Areas for scan_fraction and Its Caller

21. 6.5 A Program with Multiple Functions CASE STUDY Arithmetic with Common Fractions

23. 6.5 (cont) Case Study: Arithmetic with Common Fractions
Design
Initial Algorithm
1.Repeat as log as user wants to continue
2. Get a fraction problem
3. Compute the result
4. Display problem and result
5. Check if user wants to continue
Refinement
2.1 Get first fraction
2.2 Get operator
2.3 Get second fraction

24. 6.5 (cont) Case Study: Arithmetic with Common Fractions
Design
Refinement
3.1 Select a task based on operator
Add the fractions
3.1.3 Add the first fraction and the negation of the second
3.1.4 Multiply the fractions
3.1.5 Multiply the first fraction and the reciprocal of the second
3.2 Put the result fraction in reduced form

25. 6.5 (cont) Case Study: Arithmetic with Common Fractions
Design
Refinement of 3.2
3.2.1 Find the greatest common divisor (gcd) of the numerator and denominator
3.2.2 Divide the numerator and denominator by the gcd
Fig shows the data flow among the steps

26. Figure 6.11 Structure Chart for Common Fraction Problem
HW5

27. 6.5 (cont) Case Study: Arithmetic with Common Fractions
Implementation (Figure 6.12)
stub
A skeleton function that consists of a header and statements that display trace messages and assign values to output parameters
Enables testing of the flow of control among functions before this function is completed
multiply_fractions and find_gcd use stubs

28. Figure 6.12 Program to Perform Arithmetic Operations on Common Fractions
直接看程式…

29. Figure 6.12 Program to Perform Arithmetic Operations on Common Fractions (cont’d)

30. Figure 6.12 Program to Perform Arithmetic Operations on Common Fractions (cont’d)

31. Figure 6.12 Program to Perform Arithmetic Operations on Common Fractions (cont’d)

32. Figure 6.12 Program to Perform Arithmetic Operations on Common Fractions (cont’d)

33. Figure 6.12 Program to Perform Arithmetic Operations on Common Fractions (cont’d)

34. Figure 6.13 Sample Run of a Partially Complete Program Containing Stubs

35. Testing (Figure 6.13)
Insert a stub for each function not yet completed
Each stub prints an identification message and assigns values to its output parameters

36. 6.6 Debugging and Testing a Program System
The number of statements in a program system grows, the possibility of error also increases.
keep each function to a manageable size
Top-down testing
the process of testing flow of control between a main function and its subordinate functions
Bottom-up testing
The process of separately testing individual functions of a program system
Unit test
A test of an individual function
System integration tests
Testing a system after replacing all its stubs with functions that have been pretested

37. Figure 6.15 Driver for Function scan_fraction
A short function written to test another function by defining its arguments, calling it, and displaying its result.

38. 6.6 (cont) Debugging Tips for Program Systems
Carefully document each function parameter and local variable using comments.
Create a trace of execution by displaying names
Trace or display the values of all input and input/output parameters
Trace or display the values of all function outputs after returning from a function
Make sure that a function stub assigns a value to the variable pointed to by each output parameter
Use “step into” and “step over” in debugger

39. 6.7 Common Programming Errors
N O T
Beware of name scope and life time
Is there any identifier referenced outside its scope?
Does the identifier refer to what you want to? …