1.8

1.8

1. Translation of code

   • A translator converts the source code/high level code into a low level code ready for execution
   • Assembler
     • A assembler program converts a program written in assembly language into machine code
   • Compiler
     • A compiler translates the entire high level programming language into machine code prior to execution
     • High level lines of code can translate to many different machine code commands, whereas one assembly line of code translates to one command in machine code.
     • Adv: Executable code executes faster
     • Compiled program can be re-run without further translation.
   • Interpreter
     • An interpreter converts high level language code one line at a time, into machine code.
     • Adv: Useful for debugging
     • Interpretation has to be repeated each time the program is run

2. Compilation process

   • Lexical Analysis
     • Comments/spaces are removed
     • Keywords, constants and identifiers replaced by tokens
     • Symbol table is created holding the address of variables
       • Identifier and reserved word table produced
   • Syntax Analysis
     • Tokens checked to see if they match the spelling/grammar expected using standard language definitions
     • If syntax errors are found, error messages are produced
     • Uses BNF rules/ syntax diagrams
   • Semantic analysis
     • Variables are checked to ensure that they have been properly declared and used
     • Variables are checked to ensure they are of the correct data type
     • Operations checked to ensure they are legal for the type of variable being used (e.g. the result of an integer division is stored as an integer)
   • Code generation
     • Machine code is generated
     • A linker editor makes sure previously compiled libraries are loaded into the program at compilation
   • Code Optimisation
     • The code is improved if necessary to make it more efficient
   • Errors
     • Translation errors occur when source code is being compiled
       • Examples: Syntax errors, semantic errors
     • Execution errors occur when the program is running
       • Examples: Truncation error, logical error (negative number for age), rounding error

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