1. Computer Systems Nat 4/5 Computing Science Translator Programs

2. Lesson Aims  By the end of this lesson:  All pupils will be able to:  Describe and compare the following types of languages:  Machine Code  High Level Languages  Describe why High Level Languages require translation.  Describe how interpreters and compilers function.

3. Types Of Languages  Machine Code is made up of only 2 symbols.  1 and 0 (On and Off)  High Level Languages such as Visual Basic are written using some English words.  They are not written IN english! Nat 4/5

4. High Level Languages Nat 4/5 General Purpose Pascal, C, C++ and COMAL ALGOL (Initially used for Mainframes) Artificial Intelligence PROLOG (PROgramming in LOGic) LISP (Probably 2 nd oldest language still in use - 1958) Education Pascal COMAL BASIC Operating Systems C C++,C#

5. Why do we need them?  The source code you write is instructions for the computer  They are in a High Level Language  The computer needs these instructions translated into machine code  It’s the only language it understands! Nat 4/5

6. Types of Translators  These programs convert High Level Language Source code into machine code (binary)  Interpreter  Translates and executes one line at a time  Compiler  Translates and executes the entire program at once  This program can then be ran repeatedly Nat 4/5 Think complete!

7. Interpreter  Functions like a spoken language interpreter.  Translates and executes a single line at a time  The interpreter is ALWAYS loaded in memory  Error feedback is provided line by line  Like in Smallbasic  Interpreted programs have to be re- interpreted every single execution Nat 4/5

8. How an interpreter works Nat 4/5 Original Source Code Pctoutput.print “Hello” Pctoutput.isible = true Interpreter 1001 1000 1100 1110 0011 Syntax Error

9. How the compiler works Nat 4/5 Original Source Code Pctoutput.print “Hello” Pctoutput.isible = true Compiler 1010 1010 1010 0111 0011 1001 1000 1100 1110 0011 Syntax Error Object Code Can be saved and ran later

10. Summary  Compilers translate source code once into an executable program  Only has to be translated once!  Cannot see the source code in a compiled program  Interpreters translate source code line by line  Always has to be re-interpreted  Spots errors line by line Nat 4/5