Software Engineering for Students A Programming Approach

122 Chapter 10 ■ Data structure design
will need statements to print a heading, print a transaction line and so on. But we can
also see that we will need:
■ a loop to print a number of pages
■ a loop to print the set of transaction lines on each page.
You can see that this description of the program structure matches the structure of
the report. What we have done is to derive the structure of the program from what we
know about the structure of the report.
These small examples show how it is possible to approach program design using the
structure of data. We will return to these examples later, showing exactly how the
method treats them.
10.2 ● A simple example
Let us consider the design of a program to display the following pattern on a computer
screen. We will assume that, in drawing this pattern, the only possible cursor
movements are across the screen from left to right, and down to the beginning of a
new line.
*
***
*****
*****
***
*
The first step in the method is to analyze and describe the structure of the information
that the program is to create. The product of this step is called a data structure
diagram. The diagram for the pattern is given in Figure 10.1.
Top half
Picture
Middle
Bottom
half
* *
Line Line
Figure 10.1 Data structure diagram for the asterisks pattern