7. Programming

7. Programming

1. Algorithms are a series of steps to solve a problem

   • Flowchart
   • Pseudocode

2. Control Flow

   • Sequence - the order in which the steps need to happen
   • Selection
     • IF...THEN...ELSE, allows you to choose between 2 choices
     • Nested If Statements
   • Iteration
     • FOR Loop
     • REPEAT Loop
     • WHILE Loop

3. Programming Languages

   • 3rd Generation = High Level Languages such as Python (uses Statements)
     • Portable, will work on different machines
     • designed with a type of problem in mind
     • One high level program instruction will be translated into several machine code instructions
   • 2nd Generation = Assembly Language such as Little Man Computer (Uses mnemonics)
   • 1st generation = Machine Code such as Binary (uses 0's &1's)
     • designed with hardware in mind
     • one instruction set per processor
     • wont work on another machine
   • Translating programs into machine code
     • Must happen so it can run on the processor
       • Assemblers - convert assembly language into machine code. A simple conversion as every assembly language instruction is translated into a machine code instruction
       • Compliers & Interpreters - convert high level programming language into machine code. This is a more complex translation, as a single instruction can result in many machine code instructions
         • Compliers
           • Translates the whole program to produce the executable object code
           • The object code runs in the version that the computer runs
           • Faster run time because the program is already in machine code
           • Customers can not see the actual code
           • Used for distributed software
         • Interpreters
           • Translates and executes one line at a time
           • The source code is the version that the computer runs
           • Slower run time because the program is translated every time it is run
           • If you distributed source code with an interpreter then customers would have your actual code
           • Used in development

4. Handling data in Algorithms

   • Constants are certain values that remain the same while the program runs , i.e. VATRate=0.2,
     • Identifier, a unique name given to a value
     • declared at the start of a program
   • Variables
     • Has an identifier which refers to a location in memory where the data item will be stored
     • Declared at the start
     • Data types
       • Integer
         • A whole number
           • DIV
           • MOD
       • Real
         • A numbers with a fractional part
       • Char
         • A single character
       • String
         • zero or more characters
       • Boolean
         • True/ False

5. Arrays, a group of data items of the same data type , which is stored under one identifier

   • Benefits
     • Code is easier to follow and therefore easier to debug
     • A group of data items can be easily processed using a for loop

6. Errors

   • In a high level language a translator will scan each line of code
     • Syntax errors - mistakes typing the code i.e. prnt instead of print
     • Logical error - the code runs but does not do what you want

7. Testing

   • Normal data
   • Erroneous data
   • Boundary/ extreme data

8. IDE Tools

   • Integrated Development Environment , allows you the write the code more easily
     • WYSIWYG
       • What you see is what you get
     • Editing environment
       • colour coding key words
       • Numbering of lines
     • The feedback you see when you try to run the program is provided by the runtime environment
     • Break point - allows the program to stop the program from running at a certain point to allow them to check the values of certain variables
     • Translator - translates the code into machine code
     • Recognises comments put into the program by the developer