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.


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.

Menu BarMenu BarFilenameFilename

Immediate Window

Immediate Window

WORK AREA

FORMAT IN WRITING PROGRAM LINES

LINE NO. PROGRAM STATEMENT

10 CLS

Space

10 CLS

500 END

10 CLS

20 DISPLAY 12

500 END


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 DISPLAY 12

500 END

10 CLS

20 PRINT 12

500 END

Change 12 by any number

10 CLS

20 PRINT LORA

500 END


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

Recall MS Excel!


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.

10 CLS

20 PRINT LORA

500 END


QBASIC COMMANDS

1. CLS – clears the screen

2. END – terminates the program

3. PRINT – displays the result of computer processing

Education

Introduction to programming