programming-for-dummies

22
Figuring Out Programming
Big companies, like Microsoft and Adobe, can afford to pay programmers to
write and modify programs to run under different operating systems, such as
Windows and Mac OS X. Most smaller companies and individuals don’t have
the time to rewrite a program to run under multiple operating systems. That’s
why most small companies write programs for Windows because it’s the
largest market. If the program proves popular, they can later justify the time
and expense to rewrite that program and compile it to run under Mac OS X.
Choose your compiler carefully. If you use a compiler that can create only
Windows programs, you may never be able to re-compile that program to run on
a different operating system, such as Linux or Mac OS X. One reason Microsoft
gives away their compilers for free is to trap people into writing programs that
can run only under Windows. For example, if you write a program with
Microsoft Visual Basic, you can’t run that program on Mac OS X without major
modifications, which most people will probably never do.
Translating source code with an interpreter
In the old days, compilers were notoriously slow. You could feed source
code to a compiler and literally come back the next morning to see if the
compiler was done. If you made a single mistake in your program, you had to
correct it and re-compile your program all over again — with another
overnight wait to see if it even worked.
Trying to write a program with such slow compilers proved maddening, so
computer scientists created something faster called an interpreter. Just like a
foreign language interpreter who listens to each sentence you speak and
then translates that sentence into another language, a computer interpreter
does the same thing.
Type a program command into an interpreter, and the interpreter immediately
translates that command into its equivalent machine language command.
Type in another command, and the interpreter translates that second
command right away.
The problem with interpreters is that they only store the equivalent machine
language commands in memory instead of in a separate file like a compiler
does. If you want to sell or distribute your program, you have to give people
your source code, along with an interpreter that can convert your source
code into machine language commands. Because giving away your source
code essentially means giving away your program, everyone who wants to
sell their programs uses a compiler instead of an interpreter.
The original reason why computer scientists developed interpreters was
because compilers were so slow. But after computer scientists started creating
faster compilers, most people stopped using interpreters and just used
compilers. Nowadays, computer scientists use interpreters for running