Lexical Analysis
- Comments and unneeded spaces are removed
- Keywords, constants and identifiers are replaced by tokens
- A Symbol Table is created which holds the address of variables, labels and subroutines
- Creates new table entries in the symbol table
Syntax Analysis
- Tokens are checked to see if they match the spelling and grammar expected, using standard language definitions
- Parsing each token to determine if it uses the correct syntax for the programming language
- If syntax errors are found, error messages are produced./ if no errors are found the compilation process continues
- Adds information regarding attribute type, scope, line of reference, etc in the symbol table.
Semantic Analysis
- Variables (are checked to ensure that they) have been properly declared and used
- Variables (are checked to ensure that they) are of the correct data type
- Operations are (checked to ensure that they are) legal for the type of variable being used
Code Optimisation
- high-level general programming constructs are replaced by very efficient low-level programming codes
OBJECTIVES
- Achieve the required output of the program
- Not delay the compilation process
- Increase speed of the program
- Decrease resources demand
Code Generation
Machine code is generated
Translator
A computer program used to convert a program from one languate to another
Compiler
Takes the source code of the entire program as input to produce a machine code version of the program which can be run through a single executable file
Interperter
Takes a single code instruction as input, translates and executes it
Compiler Advantages
- Can be re-run without further translation
- Executes faster than interperated code
- Machine code can be distributed without compiler being present
- Machine code is more seccure, cannot be read without a lot of reverse engineering
- Libraries can be packaged with the executable
Compilers Disadvantages
- Compilers take longer than interperating
- Errors are only reported after compilation has finished
- One error may cause many more related errors
- Recompiling after fixing an error adds time
Interperators Advantages
- Debugging will stop translation at the point where error occurs
- Complete re-compilation not needed when error found
- Easier to partially test and debug
- Can be used during program development
- Source code is visible and can be checked for security purposes, before being interperated
Interperator Disadvantages
- Associated libraries must be present for the code to run
- To execute source code the interperator needs to be installed on the running platform
- Source code needs to be present, making interllectual property harder to protect
Assembler
- Translates assembly into machine code
- Each single assembly instruction will translate to one machine code instruction
- Assembly is easier and less prone to errors than coding in binary
- Each CPU has own instruction set
Syntax Error
Occurs when a command does not folow the expected syntac of a language
Linking Error
Calling a standard function where the correct library has not been linked to the program
Semantic Error
Variable declared illegally
Run Time Error
An error that only occurs when a program is running and is difficult to foresee beofree it is compiled and run (program compiles successfully but doesnt perform correctly)
Logical Error
An error that causes a program to output an incorrect answer to what was expected
Rounding/ Truncation Error
Continued use in further calculations causes inaccuracy
