3.3.7 Programming techniques

3.3.7 Programming techniques

1. Stepwise refinement/modular programming

   • Structured programming
     • Problem split down into sub tasks
       • Makes use of procedures and functions
         • Functions, perform a single task and returns a single value
         • Procedures can return 1, none or multiple values
           • Control passed to procedure/function from main program, procedure executed and then control returned to main program
             • Called from main program
             • Data can be passed back and forth via parameters
               • Varaiables passed to functions and procedures are called arguments or parameters
                 • If called by val then parameter would not revert back to original value outside procedure
                   • But call by ref would change the variable in the procedure
               • Allows independent creation of modules
         • Can write modules in different languages
           • Can split modules between people, most skilled programmer works on hardest module
           • Save's money
         • Saves time and money
         • Can make libraries out of commonly used modules

2. Stack

   • Function or proceudre called
     • Contents of registers put into stack including the return address
       • CPU gets start address of procedure and puts in PC
         • Procedure is run
           • CPU pops contents of registers into stack including return address into PC
             • CPU continues doing what it was doing
   • A list
     • Or LIFO data structure

3. Parameters

   • Variable/ item of data passed to procedure or function to do calculations on
     • Either by ref or by val
       • If by val, any changes made in sub will not affect variable
       • If by ref it does affect the variable

4. Global variables

   • Declared in beggining of program
     • Available to every sub

5. Local variables

   • Declared in a sub
     • Only available in that sub
       • More likley to be changed/corrupted by other subroutines

6. BNF

   • Used to unambigously define the syntax of a computer language