2. Structure of procedural programs

2. Structure of procedural programs

1. define terms

   • statement- a single instruction- arithmetic or logical
   • subroutine- a block of code separate from the main program but can be called by the main program
   • procedure- a subroutine that executes the lines in there are then gives back control to the main, does not necessarily return a value
   • function- a type of subroutine that returns a value after a caluclation
   • parameter- data that is passed to a subroutine (and used by it) from the main program
   • sequence-when instructions are followed one after the other
   • selection- when the computer makes a decision as to which instruction to do, can be IF statement or a SWITCH CASE
   • iteration- instructions repeated over and over again- loop, can be FOR, WHILE, DO-WHILE
   • control structure- a block of code that tells wich order to do the instructions (loop or selection)

2. 3 basic constructs

   • sequence
     • commands go one after the other
     • follow each other in exectution
   • iteration
     • loops
     • statements executed repeatedly
     • 3 types
       • FOR
         • Count-controlled loop
       • WHILE
         • Condition-controlled loop
         • only happens when condition is fullfilled
       • WHILE UNTIL
         • Condition-controlled loop
         • runs once then checks condition
   • selection
     • decision
     • program can choose which statement to execute depending on user entry
     • Two types
       • IF- uses a condition or expression that gives a value
       • SWITCH CASE- uses variable to decide the answer

3. nested and iteration statements

   • When one statement is put inside the other
   • indent one statement inside the other
   • can nest both loop and if statements

4. subroutines

   • a small piece of code that is separate from the main program but is called from the main program, can be two types:
     • Procedure- does the instructions then gives control back to the main program
     • Function- same as procedure but returns an answer
   • advantages
     • Can call the subroutine makes time- does not make the program any longer
     • program easier to understand and maintain- less clutter
     • Easy to test- only need to test the subroutine
     • Can reuse the subroutine over and over again
     • if there is an error only need to change in one place
   • parameters- data passed from the main program and then used by the subroutine
   • scope- how long a variable can be used for
   • variables: Local- can only be used in the subroutine, Global- can be used anywhere in the whole program

5. recursive vs. iterations

   • a subroutine that calls itself
   • needs a stopping condition to stop it or will carry on forever...
   • To solve:
   • difference between iteration and recursion
     • iteration:
       • loop repeats instructions
       • includes a tracking variable so ends
       • uses less memory as there is only 1 function so 1 set of variable
       • More complex
       • count variable needs to be initialised before the loop starts
     • recursion:
       • uses a loop too
       • uses less code
       • runs slowly
       • may run out of memory so the computer could crash
       • hard to trace
       • Need a stopping condition or never stops

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