Program Constructions

• Program Translator


  Compilers, Interpreters, Assemblers
• Compilation process


  1. Lexical analysis

  2. Syntax analysis

  3. Semantic analysis

  4. Code generation

  5. Code optimisation
• Source code


  Written by programmers in a high-level programming language
• Translators


  Convert source code into object code (machine-readable form)
• CPUs can only process 1's and 0's (machine code)
• Machine Code


  Very low level language made up of coded instructions and data
• Assembly Language


  Low level language with a small set of commands representing machine code, uses mnemonics
• High Level Languages


  Easier for programmers to use than assembly language
• Assembler


  Converts low level assembly programming language into machine language
• Interpreter


  Converts high-level language program into machine code and executes it line by line
• Compiler


  Translates a high level language program (source code) into machine code (object code) for execution at a later time
• Benefits and drawbacks of compilers and interpreters

  • Interpreters are easier to use as errors are reported and corrected as execution continues
  • Interpreters are slower than compilers as they translate the same statements repeatedly
  • Compilers can produce more efficient object code than interpreters
  • Compilers require analysis and code generation only once
• Keywords


  • Reserved words in the programming language with special meanings (e.g. if, else, while, for)
• Identifiers


  • Symbols referring to names of variables, functions, classes etc.
• Constants


  • Specific values in the source code representing numbers, characters, strings, or Boolean values
• Operators


  • Symbols used to perform operations on data (e.g. arithmetic, comparison, logical)
• Token


  Numeric representation of keywords and identifiers in lexical analysis
• Parsing


  Analysing the structure of the source code based on the grammar of the programming language
• Compilation process


  1. Lexical analysis

  2. Symbol table construction

  3. Syntax analysis

  4. Semantic analysis

  5. Code generation

  6. Code optimisation
• Programming errors


  • Logical
  • Syntactical/Syntax
  • Runtime/execution
  • Linking
  • Rounding
  • Truncation
• Logical errors


  • Cause incorrect output without crashing the program, harder to detect than syntax errors
• Syntax errors


  • Occur when a command does not follow the expected syntax of the programming language
• Runtime/execution errors


  • Occur when the program is running and are difficult to foresee before compilation
• Linking errors


  • Occur when a programmer calls a function but the correct library has not been linked/imported
• Rounding


  Approximating to the nearest whole number/tenth/hundredth etc.
• Truncation


  Approximating to the nearest whole number/tenth/hundredth etc. by removing decimal places