structure-charts

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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:

Flowchart of login process: input username, enter password, check password with conditions, possible outputs are "Login successful" or "Access denied".

Key features

Feature	Explanation
Top-down design	The chart starts with the main program and breaks it into sub-modules
Decomposition	Each module represents a specific task or function
Module boxes	Each module is shown as a box
Vertical lines	Show control flow – which module calls which
Parameter arrows	Arrows pointing into modules show data being passed in or returned
Stepwise refinement	Each level adds more detail to the task above
Diamond shape	Shows a condition that could be true or false
Semi-circular arrow	Indicates repetition

Pseudocode from structure chart

The first step is to create an identifier table

Identifier	Data type	Description
`Username`	STRING	Stores the username entered by the user
`Password`	STRING	Stores the password entered by the user
`StoredPass`	STRING	The correct password stored in the system for comparison
`NoAttempts`	INTEGER	Counts the number of failed login attempts
`LoginSuccess`	BOOLEAN	Indicates whether the login was successful

Next, identify is any functions or procedures could be used

Module	Type	Purpose
`GetCredentials`	PROCEDURE	Asks the user to input username and password
`CheckPassword`	FUNCTION	Compares input password with stored password and returns TRUE/FALSE
`ShowAccessMessage`	PROCEDURE	Displays success or failure message

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)

Computer-science_A-level_Cie

structure-charts

Structure charts

What is a structure chart?

Example

Key features

Pseudocode from structure chart

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