A-level Computer Science₇₅₁₇

Understand the concept of a data type.

Understand and use the following appropriately:

• integer
• real/float
• Boolean
• character
• string
• date/time
• pointer/reference
• records (or equivalent)
• arrays (or equivalent).

Variables declared as a pointer or reference data type are used as stores for memory addresses of objects created at runtime, ie dynamically. Not all languages support explicit pointer types, but students should have an opportunity to understand this data type.

Define and use user-defined data types based on language-defined (built-in) data types.

Use, understand and know how the following statement types can be combined in programs:

• variable declaration
• constant declaration
• assignment
• iteration
• selection
• subroutine (procedure/function).

The three combining principles (sequence, iteration/repetition and selection/choice) are basic to all imperative programming languages.

Use definite and indefinite iteration, including indefinite iteration with the condition(s) at the start or the end of the iterative structure. A theoretical understanding of condition(s) at either end of an iterative structure is required, regardless of whether they are supported by the language being used.

Use nested selection and nested iteration structures.

Use meaningful identifier names and know why it is important to use them.

Be familiar with and be able to use:

• addition
• subtraction
• multiplication
• real/float division
• integer division, including remainders
• exponentiation
• rounding
• truncation.

Be familiar with and be able to use:

• equal to
• not equal to
• less than
• greater than
• less than or equal to
• greater than or equal to.

Be familiar with and be able to use:

• NOT
• AND
• OR
• XOR.

Be able to explain the differences between a variable and a constant.

Be able to explain the advantages of using named constants.

Be familiar with and be able to use:

• length
• position
• substring
• concatenation
• character → character code
• character code → character
• string conversion operations.

Expected string conversion operations:

• string to integer
• string to float
• integer to string
• float to string
• date/time to string
• string to date/time.

Be familiar with, and be able to use, random number generation.

Be familiar with the concept of exception handling.

Know how to use exception handling in a programming language with which students are familiar.

Be familiar with subroutines and their uses.

Know that a subroutine is a named ‘out of line’ block of code that may be executed (called) by simply writing its name in a program statement.

Be able to explain the advantages of using subroutines in programs.

Be able to describe the use of parameters to pass data within programs.

Be able to use subroutines with interfaces.

Be able to use subroutines that return values to the calling routine.

Know that subroutines may declare their own variables, called local variables, and that local variables:

• exist only while the subroutine is executing
• are accessible only within the subroutine.

Be able to use local variables and explain why it is good practice to do so.

Be able to contrast local variables with global variables.

Be able to explain how a stack frame is used with subroutine calls to store:

• return addresses
• parameters
• local variables.

Be familiar with the use of recursive techniques in programming languages (general and base cases and the mechanism for implementation).

Be able to solve simple problems using recursion.

Understand the characteristics of the procedural- and object-oriented programming paradigms, and have experience of programming in each.

Understand the structured approach to program design and construction.

Be able to construct and use hierarchy charts when designing programs.

Be able to explain the advantages of the structured approach.

Be familiar with the concepts of:

• class
• object
• instantiation
• encapsulation
• inheritance
• aggregation
• composition
• polymorphism
• overriding.

Students should know that:

• a class defines methods and property/attribute fields that capture the common behaviours and characteristics of objects
• objects based on a class are created using a constructor, implicit or explicit, and a reference to the object assigned to a reference variable of the class type
• in the Unified Modelling Language (UML) composition is represented by a black diamond line and aggregation by a white diamond line.

Know why the object-oriented paradigm is used.

Be aware of the following object-oriented design principles:

• encapsulate what varies
• favour composition over inheritance
• program to interfaces, not implementation.

Students would benefit from practical experience of programming to an interface, but will not be explicitly tested on programming to interfaces or be required to program to interfaces in any practical exam.

Be able to write object-oriented programs.

Practical experience of coding for user-defined classes involving:

• abstract, virtual and static methods
• inheritance
• aggregation
• polymorphism
• public, private and protected specifiers.

Be able to draw and interpret class diagrams.

Class diagrams involving single inheritance, composition (black diamond line), aggregation (white diamond line), public (+), private (-) and protected (#) specifiers.