Programming

Programming

1. Languages

   • High level languages
     • allows code to be to be witten
     • easy for humans to understand
     • examples
       • Basic
       • Java
       • Pascal
       • COBOL
       • C#
       • C++
     • Can complete complex tasks
   • Machine code
     • doesn't resemble any natural language instead made up of bit patterns
     • High level languages need to be converted into machine code before executed by the CPU
     • Examples
       • opcode
       • Operand

2. Variable

   • store data that can change given a idenifier/ name
   • Local
     • defined and accessed only within the same sub procedure
   • Global
     • variables thant can beaccessed anywhere within a program
   • Static
     • variable that lasts the running programs lifespan
   • Dynamic
     • lifespan ends when the sub procedure it was defined in ends

3. Constant

   • store data that does not change
   • i.e PI

4. Assembelers

   • a program which converts low level assembly code into machine code
   • done by converting one word assembly instructions into opcode
   • It also allocates memory to varieables resulting in operand

5. Interperaters

   • before running high level programming language it is converted by an interpreter on line at a time into machine code which is then executed by the CPU

6. Compilers

   • used to convert high level programming languages into machine code
   • 4 main stages
     • lexical analysis
       • syntax anylasis
         • semantic anylisis
           • code generation
             • generate machine code
             • code optimisation employed to make more efficient/faster/less resource intensive
           • check variables for if properly declared and used
           • variables checked for id correct data type
           • operations are checked to ensure legal for type of variable
         • tokens are checked to match expected syntax
         • If syntax errors found, error messages produced
       • comments and un-needed spaces removed
       • keywords , constants and identifiersreplaced by tokens
       • symbol table created to hold addresses of variables, labela and subroutines

7. translaters

   • changes a program written in one language to another

8. Types of errors

   • Syntax
     • error that occurs when a command line dosnt follow expected language syntax
     • spelling mistakes ADN instead of AND
   • Runtime/ execution
     • error that only occurs when a program is running and is difficult to foresee before compiling and running
     • if a program needs more memory room so it crashes as it runs out
   • Logical
     • error that causes a program to output an incorrect answer
     • if a program gives out a negative number for someones birth date
   • Linking
     • an error that occurs when a programmer calls a function within a program and the correct library has not been linked to that program
     • square root function used but the library holding how to do this is not linked
   • Rounding
     • when a number is approximated and rounded to a number
     • 2368 rounded to 2370
   • Truncation
     • number approximated to a whole number
     • 34.9 truncated to 34