Introduction to programming

Introduction
to
Programming

Computer Program
• A computer program is nothing more
than a list of instructions that tell the
computer what to do.
• A computer program is an organized
list of instructions that are designed to
cause the computer to behave in
predetermined manner in order to
accomplish a task.

Introduction to Programming

Computer Program
Windows OS with all its
icons, toolbars, and menus is really
nothing more than a series of instructions
that the computer follows each time you
press a button, click on a menu, or
respond to a dialog box.
At the base level, all programs
accept input from the user, process the
data, and display, save or print the results.


Goals of a Program

• Be easily read and understood
• Be easy to correct if problems arise
• Be easy to modify as elements in
the task may change
• Function as it was intended, to
solve a specific problem or perform
a specific task


Programming
Language
A programming language is a
vocabulary and set of grammatical
rules for instructing a computer to
perform specific tasks.
These grammatical rules are
also called the syntax of the
language.


Programming
Languages
1. Machine languages
2. Assembly languages
3. High-level languages
4. Fourth-generation languages


Machine languages
Machine languages use binary to
provide instructions to the computer.
Machine languages are not
common today as they are specific to
each CPU and require long lists of
zeros and ones.
These programs are very difficult to
write and very error-prone.


Assembly languages
Assembly languages use a special
representation of instructions to give
the computer instructions.
These languages are only used by
programmers developing complicated
processes like operating systems.


High-level languages
High-level languages use English-
like commands to give instructions.
They include
BASIC, Pascal, C, C+, C++, COBOL, Java,
JavaScript and Fortran.
Of course, the computer does not
speak English.
It speaks binary, therefore the
programming instructions written in a high-
level language must be converted into
binary using a compiler or interpreter.


Interpreters vs.
Compilers
Interpreters translate programs
one line at a time while compilers
convert a whole file or program at
once and then generate a separate
executable file.
The executable file usually ends
with the extension .exe and can be
run without the programming
language.


Fourth-generation
languages
Fourth-generation languages are
languages that write code for the user
through a series of menus and
prompts.
Some examples of fourth
generation languages include
ORACLE, and Visual BASIC.


Common Features of
Programming Languages

There are many programming
languages that can be used to
create a computer program.
Each of these languages has
different syntax.
However, a basic set of
instructions is always present in
any programming language.


Basic Set of Instructions

1. Input
2. Output
3. Mathematics
4. Conditional execution
5. Repetition


BASIC Language

BASIC stands for Beginner's All-
Purpose Symbolic Instruction Code.
It is developed in the mid-1960s
at Dartmouth College by Professors
John G. Kemeny and Thomas E.
Kurtz.


Why Study BASIC?
When you learn BASIC, you also
learn many of the fundamentals of
other programming languages.
You can also create programs
easily.
Once you get into it, you'll find
that the fun in creating programs is
worth coming back to.


QBASIC
QBASIC is a programming
language written for computers back
in 1975, by Bill Gates and Paul Allen.


Filename
Menu Bar

Immediate
Window

FORMAT IN WRITING
PROGRAM LINES

LINE NO. PROGRAM STATEMENT

10 CLS

Space

Errors in Programming
If you made any mistakes you will be
given an error message.
The error message, also called a
diagnostic message, will indicate the line
number and a description of the error.
At this point, you will have to do what
is called debugging.
Programmers spend a great deal of
time debugging programs.


Debugging
Debugging is the process of
finding and fixing errors in a program.
The word debugging comes
from a common computer problem in
the 50's. Bugs would fly inside the
computer.
Technicians had to find and
remove them in order for the system
to work.This word is still in use today.


Types of Programming
Errors
1. Syntax errors
2. Logic errors


Syntax Error
A syntax error is a mistake in the
grammar or structure of a command.
For example, in QBASIC, the syntax
for PRINT says you must type PRINT, a
space, and then the literal, number or
expression.
If by mistake you omit the command
PRINT, then the command will not work.
This is a syntax error.


Syntax Error

All syntax errors are captured by
the compiler or interpreter.
When you get a syntax error in
your program, you should read and
decipher the error message, then
move to the line identified and fix the
error.


Logic Error
A logic error is much more difficult to isolate
and fix.
A logic error is a mistake that the compiler
or interpreter cannot identify.
This kind of error occurs when your
instructions have no syntax error, but the program
does not accomplish its intended purpose.
For example, if you were asked to find the
area of a circle, but instead calculated the
circumference of a circle, then you would have a
logic error.


Correcting Logic Error
The only way to determine a logic
error is to test your program.
You should check if the program
works correctly, figure out what the answer
should be (on your own), then check your
answer with the result the program
provides.
If the computer provides a wrong
answer, then you will have to examine your
program to locate and fix the error.


Save your program!
Once you have found your error and
corrected it, rerun your program.
When all errors are fixed, save the
file. To do this, press ALT + F (“File“) and
then press S("Save“). Your file will be
saved with the name you provide and will
end with the extension .bas.
The maximum number of characters
for the QBASIC program filename is eight.


10 CLS
20 PRINT 12
500 END

Change 12 by any number

Recall your Algebra!

Constants and Variables
Constants are represented by
numerals.
Examples: 5, -3, 4.56, - 13.9
Variables are represented by letters.
Examples: x, y, n, C, F


MS Excel Formula

In MS Excel, a cell can contain
formula.
Example: Cell C1 contains =A1 * B1
A1 and B1 are cell addresses.
They can be used as variables in a
formula.


Variable Names

In Algebra, x + y means x is
increased by y.
In Algebra, xy is the product of x and
y.
In QBASIC, xy is only a single
variable name and NOT a
product of x and y.


QBASIC COMMANDS
1. CLS – clears the screen
2. END – terminates the program
3. PRINT – displays the result of
computer processing


Introduction to programming

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Introduction to programming