Programming Languages

Programming Languages

1. Generations

   • First Generation
     • Machine Code
       • 0's and 1's
       • Lowest Memory Usage
       • Hard to read
       • In machine code, a typical instruction holds an operation code (opcode) in first 4 bits and the operand (the data to be operated on or the address where the data is held) in the second 4 bits
   • Second Generation
     • Assembly Language
       • Combines machine code statements to form arguments and functions.
       • Easier to understand and allows for better memory
       • Can be long and hard to do.
       • Machine code with words. Each command translates directly into one command in machine code Most of the commands are mnemonics, e.g. LDR Load Register STR Store Register ADD, SUB The assembly code is known as source code and this is translated into object code (compiled code) by an assembler.
   • Third Generation
   • Fourth Generation
   • Natural Language
     • English
     • French
     • German
     • Spanish
     • Polish
     • Welsh
     • A language that has developed naturally through use, it contains grammar and syntax
   • Low Level
     • Less readable than code written in a high-level language and so more difficult to understand, maintain and debug. Less readable than code written in a high-level language and so more difficult to write without making errors Machine dependent making it difficult to port to a different instruction set processor compared with code written using a high-level language which do port readily because they are not machine-oriented.

2. Hierarchy

   • High Level Languages
     • Imperative
       • Procedural
       • Object Oriented
       • Imperative programs are made up of sequence, selection and iteration blocks (“Every program is just a step, a branch and a loop”)
       • Limitation of imperative programming is that it doesn’t deal well with ideas and concepts.
     • Declarative
       • Functional
       • Database Query
       • Logic
       • Functional programming treats procedures as mathematical functions. The building blocks are functions rather than instructions.
       • Declarative programs describe the desired results of the program (what it should accomplish), without explicitly listing command or steps that need to be carried out to achieve the results.