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Summary GCSE Computer Science notes
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Detailed notes on Programming, Fundamentals of Data Representation, Fundamentals Of Algorithms, Computer Systems, Networks in the AQA GCSE Computer Science course.
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Data TypesA variable is a memory location holding a data item which may change value during
program execution.
A constant is a memory location holding a data item which cannot change during program
execution.
Data Type Type of data Examples
Integer A whole number 3, -170, 164000
Real / Float A number with a decimal point 3.142, 78.0 , -0.85
Character / Char A single character or symbol that can be typed A, #, @, 6, !
String Zero or more character enclosed in speech marks “Yes”, “hello”, “”
Boolean Can only take the value True or False True, False
Programming Concepts
Selection - changing the direction of a program based on a specific criteria (IF, ELSE, ELIF)
Sequence - the idea of one step being done after another in a particular order
Iteration - repeating sections of code in a loop (FOR, WHILE, REPEAT)
Variable declaration - Saying what the data type will be and where it’ll be stored in memory
Assignment - Alters the value of a variable
Subroutines
Subroutine - A subroutine is a named block of code, separate from the main program, which
can be executed by writing its name in a program statement.
● Function: Subroutine which will return a single result
● Procedure: Subroutine that does not return a value
Advantages of using subroutines:
- Subroutines can be tested separately
- A subroutine can be called several times in the same program and can be stored in a
subroutine library to be used in other programs
, Structured approach to programming
The structured approach to programming includes modularised programming using
parameters and local variables. Clear well - documented code should include
comments to explain what the code is intended to do. Decomposition can be used to help
produce structured code.
Local and global variables
Variables created within a subroutine are called Local Variables. These are only available
for use in the function or procedure and once the subroutine ends, they are destroyed.
Variables created outside of a procedure or function are known as Global Variables. It is
best to avoid using these as they take up memory and increase the chance of naming
clashes which could lead to bugs.
Advantages of modular programming
- Programs are more easily and quickly written
- Large programs are broken down into subtasks that are easier to program and
manage
- Each module can be individually tested
- Modules can be re-used several times in a program
- Makes large programs are much easier to debug and maintain
Robust and Secure programming
Data Validation
Length check - A string entered by a user must be greater than or equal to a minimum
length
Presence check - A string should not be empty. Checking if there is a specific item in the
string.
Range check - Data must lie within the given range (e.g 1 - 10)
Authentication Routines
Authentication is a process used to test that a person is who they claim to be. Methods of
authentication include usernames and passwords, a PIN number or more complex biometric
methods. This helps to prevent unauthorised access.
, Representing Algorithms
Algorithm - An algorithm is a sequence of steps that can be followed to complete a task
Decomposition - Breaking down a problem into smaller, more manageable parts which are
easier to solve.
Abstraction - Removing unnecessary details from a problem
Searching Algorithms
Linear Search
Searches through a list of items one at a time in a linear way until the given item is found. If
the given item is found the search will return True. If the given item is not found after all
iterations, it will return False. The list does not need to be sorted.
Binary search
Goes to the middle of the list, decides whether the item is greater than, less than or equal to
the item that’s being looked for. If it’s greater than or less than then it will go to the
corresponding half of the list to begin the search process again. If the item matches the
number you're searching for it'll return True. Otherwise repeat these steps above until it has
searched the list. If it's not in the list return False.
Linear vs Binary Search
- Linear search is a simpler algorithm
- Linear search does not need to be sorted
- Binary search is much quicker than Linear
Sorting Algorithms
Bubble sort
A bubble sort works by repeatedly going through the list to be sorted, swapping adjacent
elements if they are in the wrong order
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