# A-level Computing 2009/AQA/Problem Solving, Programming, Data Representation and Practical Exercise/Skeleton code/2013 Exam/Section C
## Validation

* Error Checking
* List the Erroneous, Extreme and Typical Data for a user selecting a menu item:
* Answer:
* Erroneous data – Anything other than “a, b, d, e, g, h, n” (in the original program, an example would be “z” or “2”).
* Extreme data-
* Typical data – Letters “a, b, d, e, g, h, n” (in the original program).
* List the Erroneous, Extreme and Typical Data for Caeser Cipher Offset:
* Answer:

## Variables

* Variables
* State one advantage of using named constants for constant values
* Answer:
* Improves readability of code // Easier to update the programming
* code if the value changes ( A. by implication) // reduce the likelihood
* of errors;
* Give the identifier of a local variable
* Answer:
* Any from;
* Ciphertext, Plaintext, Choice, AmountToShift, StartPosition, EndPosition, SizeOfRailFence, N,MenuChoice, TextFromUser, CharacterFromFile, TextFromFile, Count, Key, TypeOfCharacter, ChangedText, ASCIICode, NoOfColumns, NoOfRows, NoOfCiphertextCharacters, NoOfCiphertextCharactersProcessed, i, j, PostitionOfNextCharacter, LastFullRowNo, AmountToReduceNoOfColumnsTimesjBy, BeginningOfNextRowIndex, HiddenMessage, CurrentPosition.
* State the name of an identifier used for a pre-defined function with a single parameter
* Answer:
* VB.net = Asc("a")
* State the name of an identifier used for a variable that is used to control the iteration of a loop
* Answer:
* Count.
* State the name of a user-defined procedure/function that has exactly 3 parameters, and name them.
* Answer:
* EveryNthCharacterSteganography(StartPosition, EndPosition, N)
* Give an example of an assignment statement:
* Answer:
* Plaintext = ""
* Give an example of a variable declaration:
* Answer:
* VB.net - Dim N As Integer
* Give an example of the use of a variable that has the role of being a Most Recent Holder :
* Answer:
* textFromUser
* Give an example of the use of a variable that has the role of being a Stepper :
* Answer:
* Count
* Give an example of the use of a variable that has the role of being a Gatherer :
* Answer:
* ciphertext

## Loops

* Loops
* Give the name of a stepper variable used in a loop?
* Answer:
* Count
* Give the name of a fixed variable used in a loop?
* Answer:
* Give the name of a follower used in a loop?
* Answer:
* Give the name of a most recent holder used in a loop?
* Answer:
* What is the purpose of nested loops?
* Answer:
* Why have they used FOR loops in the subroutine ????
* Answer:

## Sub Routines

* Sub Routine
* Write down a function declaration used in the program
* Answer:
* Write down a function call used in the program
* Answer:
* Write down a procedure declaration used in the program
* Answer:
* Give the name of a parameter used in a procedure
* Answer:
* Explain the difference between using byRef and byVal
* Answer:
* When a parameter is passed byRef, the variable inside the routine uses a reference to the same memory location as the variable passed as the parameter. When a parameter is passed byVal, the variable inside the routine copies the value of the calling code's variable to the routine's parameter.
* Why is Byref used in the ????? sub routine?
* Answer:
* ByRef is used because the procedure is then able to change the value that it was sent when it was called.
* Write down where a return value for a function is assigned:
* Answer:
* Name the flag used in the sub routine ?????? and describe its purpose
* Answer: