What is Programming?

• A program is a list of instructions that is executed by a computer to accomplish a particular task.

• Creating those instructions is programming by a programmer

• Programming language: • Special language (like French or German)• Understood by the computer• Tells the computer what to do• Used by a programmer to write a program

– Visual Basic, Java, C#, C++, COBOL

• Machine language: • Language of the computer• Every “Programmer” language is converted to machine

language• Consists of bits on or off only• Compiler or interpreter: • Software that translates programming languages to

machine language

• Coding the program:– Select the programming language– Write the instructions

• Using software to translate the program into machine language:– Programmers write instructions in English-like

high-level languages– Compilers or interpreters change the programs

into low-level machine language that can be executed

– Syntax errors are identified by the compiler or interpreter

– 1 bit (0 or 1)– 4 bits = nibble– 1 byte = 8 bits = 2 nibbles

• Is the storage for one character

– 1 word = 4 bytes– 1 K = 1 KB = 1 kilobyte = 1,0240 bytes = 210 bytes

• Kilo = 1,000 : 1 KB = 1,000 bytes

– 1 Meg = 1 megabyte (MB) = 1 million = 1024 KB – 1 GB = 1 gigabyte (GB) = 1024 MB = 1,000,000,000– Many people approximate to steps of 1000, not 1024

Binary Machine Language –

all data types consist of 1s and 0s

Programming Languages– Machine Languages

• 0110110111110111 0000000100000000 0000000100000000

– Assembly Languages• One programmer instruction converted to 1 machine level

instruction• ADD A,B

– High-level Languages• Looks more like English words and algebraic expressions• Examples of high level languages• Programmer instruction converted to many machine level

» ADA BASIC

» C++ FORTRAN

» COBOL Java

» Pascal Visual Basic

Programmer written computer code

Translator (Interpreter) Program

(browser)

Compiler Assembler

Many machine Language Instructions

One Machine Language Instruction

Execute

.exe file

Programmer written computer code

Execute

FUNCTIONBrowsersnetscapeMS ExplorerJavascriptPHPASP

MS Word, Windows XP, MS Excel, Vista, MS Explorer

Machine Language Generation

Writing Programs

• To write a program in a high-level language, you need:– Appropriate software– A text editor to type and edit program

statements– A debugger to help find errors in program

code– A compiler or interpreter to translate the

program into machine language

Error Types

• Logic errors are more difficult to locate than syntax errors

Syntax: the rules governing word usage and punctuation in the language(format, recipe, formula)

Syntax Error Cycle

• A program must be free of syntax errors to be run, or executed, on a computer

• The program will not compile or be translated• A message will point out the offending instruction

• To function properly, the logic must be correct

• The program will still execute• The output may be incorrect• The program may exit prematurely• The program may ABEND (Abnormal Termination)• The program may execute with no errors/problems

Logic• A program must be free of syntax errors to be run, or

executed, on a computer

• To function properly, the logic must be correct• What’s wrong with this logic for making a cake?

• Two major programming techniques:– Procedural programming– Object-oriented programming

• Procedural programming: focuses on the procedures that programmers create

• Object-oriented programming: focuses on objects that represent real-world things and their attributes and behaviors

• Both techniques employ reusable program modules

Mainline Logical Flow Through a Program

Procedural program: one procedure follows another from beginning to end

Mainline logic has three distinct parts:Housekeeping: steps to get ready

Main loop: instructions executed for every input record

End-of-job: steps taken at end of program

Break the logic down into at least three modules

Mainline Logical Flow Through a Program

• Modularization of the program:– Keeps the job manageable– Allows multiple programmers to work

simultaneously– Keeps the program structured

Mainline Logical Flow Through a Program

Housekeeping Tasks

• Housekeeping tasks: include all steps that occur at the beginning of the program– Declare variables– Open files– Perform one-time-only tasks such as printing

headings– Read the first input record

Annotate the Output

• If the output consists of numbers or any data that has no explanatory text with it, you should annotate your output – this means to add some text so the user knows what the output means.