Structure Charts (Cambridge (CIE) A Level Computer Science): Revision Note

Structure charts

What is a structure chart?

• A structure chart is a modelling tool used in the design stage of program development

• It helps to decompose a problem into smaller, manageable sub-tasks, representing each as a module

• Structure charts focus on what the program does, not how it does it

Example

• A program that asks a user to enter their username and password

• Checks if the password matches the stored password and uses a counter to track how many times it is checked

• If the password matches, a successful message is displayed, else after three failed attempts a 'denied' message is displayed

• A structure chart might look like:

Key features

Pseudocode from structure chart

• The first step is to create an identifier table

• Next, identify is any functions or procedures could be used

• Any finally, write the pseudocode

DECLARE Username : STRING
DECLARE Password : STRING
DECLARE StoredPass : STRING
DECLARE NoAttempts : INTEGER
DECLARE LoginSuccess : BOOLEAN

StoredPass ← "admin123"
NoAttempts ← 0
LoginSuccess ← FALSE

PROCEDURE GetCredentials()
    OUTPUT "Enter username: "
    INPUT Username
    OUTPUT "Enter password: "
    INPUT Password
ENDPROCEDURE

FUNCTION CheckPassword(P : STRING) RETURNS BOOLEAN
    IF P = StoredPass THEN
        RETURN TRUE
    ELSE
        RETURN FALSE
    ENDIF
ENDFUNCTION

PROCEDURE ShowAccessMessage(Success : BOOLEAN)
    IF Success = TRUE THEN
        OUTPUT "Login successful"
    ELSE
        OUTPUT "Access denied"
    ENDIF
ENDPROCEDURE

WHILE NoAttempts < 3 AND LoginSuccess = FALSE
    CALL GetCredentials()
    LoginSuccess ← CheckPassword(Password)

    IF LoginSuccess = FALSE THEN
        OUTPUT "Incorrect password"
        NoAttempts ← NoAttempts + 1
    ENDIF
ENDWHILE

CALL ShowAccessMessage(LoginSuccess)