101

 When you communicate with people you use a language that you both understand.  The trick is that the computer does not speak English.  To communicate with a computer you need to speak it’s language.

 The language that you use when communicating with a computer is called a ‘programming language’.  There are many programming languages out there and they all have a different style in which they talk to the computer.  The computer programming language that we will be using in this class is called ‘Scratch’.

 1GL (First Generation Language)  Speaks in the computers native language.  That’s 0’s and 1’s (binary)  What does that look like?  Why it’s good  Code is VERY FAST  Why it’s bad  Hard to read by humans

 2GL’s  Replace 0’s and 1’s with Mnemonic Codes  An Assembler converts your codes into machine code.  Why it’s good  Still very fast (1 to 1 relationship with machine code)  Why it’s bad  Code is tied to a specific processor  Still very hard to understand for a human  2GL (Second Generation Programming) LDA A ADD #5 STA A JMP # Assembler

 3GL’s  Are called ‘high level languages’  Are closer to English (or real world language’ than the mnemonics used in 2GL’s  This makes them more programmer friendly  Which makes them easier to use  Are imperative  That means code is executed line by line in the order that you write the code  In an imperative language YOU tell the computer how to do the work  3GL (Third Generation Programming)

 3GL’s  A program called a compiler converts your commands into Object (machine code)  There is NOT a 1 to 1 relationship between a 3GL command and its machine code  Compilers can create machine code that is not tied to a particular computer platform  3GL (Third Generation Programming) Compiler Source Code Object (machine) Code

 4GL’s  Are designed to decrease the amount of time it takes to create computer programs  Are declarative  That means you describe what you would like the computer to do but NOT how to do it  In an declarative language YOU tell the computer what you want it to do and it figures out how to get it done.  The line between 3GL’s and 4GL’s continues to get more blurry as computer programming languages continue to evolve.  4GL (Fourth Generation Programming)