Teach Yourself Borland C++ in 14 Days - portal

64 Day 2
NOTE
seen, I have been using getch() at the end of my programs to keep the program from closing
prematurely, but have been ignoring the return value. The getch() function returns the
ASCII value of the key pressed. Because the ASCII value of the 1 key is 49, I want to subtract
49 from the value of the key pressed to obtain the equivalent index number for that record
in the records array. If the user presses 1, an ASCII 49 is returned, and 49–49 is 0, which
is the first index of the array. If the user presses 2, the calculation yields 1 (50–49), and so on.
The do-while loop ensures that the user presses a key between 1 and 3. If a key other than
1, 2, or 3 is pressed, the loop continues to fetch keystrokes until a valid key is pressed.
Finally, I want to point out line 66 in Listing 2.4:
mailingListRecord temp = listArray[rec];
This code is not necessary in this program, but I included it to illustrate a point. This code
creates an instance of the mailingListRecord structure and assigns to it the contents of one
of the structures in the array. A simple assignment is possible here because the compiler knows
how to copy one structure to another. It does a simple member-to-member copy and copies
all structure members to the newly created instance of the structure.
Our discussion of structures up to this point describes how a structure
works in C. In C++ a structure operates like it does in C, but C++
extends structures to allow them to contain functions as well as data
members. In fact, a structure in C++ is essentially a class where all data
members and functions have public access. That won’t make sense
until later on when I discuss classes on Day 4, but you can file this
tidbit away for future reference.
Now you know about structures. Chances are you won’t use a lot of structures in your
programs. This section is important, though, because it serves as sort of a primer for
discussing classes in Day 3, “Up to Your Neck in C++.”
Summary
This chapter contains essential information on some of C++’s basic operations. You need
what is presented here in order to program in C++Builder. First you learned about the
different types of loops in C++; then you learned about the switch statement and how to use
it. I talked a little about scope and what that means to your variables. Then you found out
what structures are and how they can be used in your programs. Tomorrow we’ll tackle some
of the big stuff.