Software

Software

1. Levels of Computer Language

   • High level code
     • Much easier to use are languages like Python, Greenfoot and Scratch
       • These are all high level languages
     • This is code that is designed to be easy for humans to read and interpret
     • CPUs can’t run high level commands directly – each high level instruction needs translating in to a range of machine code instructions in order to run
   • Low Level Code
     • Low level code is executed directly by the computer
     • There are two types of low level code
       • Machine code is written entirely in binary
         • Machine code is the exact 1s and 0s that are fetched and executed by the CPU
         • Machine code consists of a list of commands, each of which has two parts
           • A binary value that represents an instruction (called an opcode)
           • The data in binary form (called an operand)
       • Assembly is written with words representing each binary command

2. Program function

   • Assemblers translate assembly language to machine code
     • Each operator and operand is replaced with its binary equivalent
     • No need for analysis of code or complex function creation
   • Compilers and Interpreters translate high level code to machine code
     • Complex translation each line of high-level code can require many machine code instructions

3. Errors

4. Stages of Compilation

   • Lexical Analysis: Comments and unneeded spaces are removed. Keywords, constants and identifiers are replaced by 'tokens'.
   • Symbol Table Construction: A symbol table is created which holds the addresses of variables, labels and subroutines.
   • Syntax Analysis: Tokens are checked to see if they match the syntax for the programming language. If syntax errors are found, error messages are produced.
   • 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 Generation: Machine code is generated.
   • Code Optimisation: Code optimisation may be employed to make it more efficient/faster/less resource intensive.

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