programming-for-dummies

Chapter 2: Variables, Data Types,
and Constants
In This Chapter
Declaring your variables
Defining data types
Storing and retrieving data in a variable
Using constant values in variables
Defining a variable’s scope
Every program consists of a list of instructions that tell the computer
what to do. The simplest program consists of a single instruction,
such as one that tells the computer to display the words, Hello, world!
on-screen.
Of course, any program that does the same thing over and over again isn’t
very useful or interesting. What makes a program useful is when it can
accept information from the outside world and then respond to that
information.
So instead of just displaying Hello, world! on-screen, a more useful program
might ask for the user to type his name in so the program could display
Hello, Bob!
Programs don’t always have to get information from a person. Sometimes,
programs can retrieve data that’s stored somewhere else, such as a list of
employees stored on another computer.
That program could access this database over a network and determine
which person has been assigned to which computer in the building. Then
the program can retrieve each person’s name so when he turns on the computer,
the program displays his name on his screen.
An even more sophisticated program could work with a Web cam hooked up
to the computer along with a database that includes employee names and
their photographs. So every time any computer’s Web cam spots someone
sitting at the computer, the program could examine the person’s image