1.3 What is Debugging
3
Working in interactive mode is convenient for testing small pieces of code because
you can type and execute them immediately. But for anything more than a few lines,
you should save your code as a script so you can modify and execute it in the future.
1.2
WHAT IS A PROGRAM?
A
program is a sequence of instructions that specifies how to perform a computa-
tion. The computation might be something mathematical, such as solving a system of
equations or finding the roots of a polynomial, but it can also be a symbolic compu-
tation, such as searching for and replacing text in a document or (strangely enough)
compiling a program.
The details look different in different languages, but a few basic instructions appear
in just about every language:
input: Get data from the keyboard, a file, or some other device.
output: Display data on the screen or send data to a file or other device.
math: Perform basic mathematical operations like addition and multiplication.
conditional execution: Check for certain conditions and execute the appropriate
sequence of statements.
repetition: Perform some action repeatedly, usually with some variation.
Believe it or not, that’s pretty much all there is to it. Every program you’ve ever used,
no matter how complicated, is made up of instructions that look pretty much like
these. So you can think of programming as the process of breaking a large, complex
task into smaller and smaller subtasks until the subtasks are simple enough to be
performed with one of these basic instructions.
That may be a little vague, but we will come back to this topic when we talk about
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