Faster execution due to direct addressing on memory address / More efficient on hardware control[DSE 2022 P2D Q1(f)]
First generation language (1 GL)
Example: Machine language
The codes of machine language consists of a series of binary numbers (0 or 1)
Programs written in machine languages can be executed by the CPU directly
It is difficult to write and maintain machine language
Machine dependent e.g. programs written for a particular type of computer cannot be executed on other types of computers
Second generation language (2 GL)
Example: Assembly language
Assembly language uses mnemonics to represent the machine language instructions
Since mnemonics are short codes that are easier to remember and use than binary codes, this makes assembly language easier to write than the machine language
Assembly language is often used in programming related to hardware, such as driver programs, and also the kernels of operating systems etc.
High-level language
Machine independent[DSE 2022 P2D Q1(f)]
Easy to write, understand, debug and maintain[DSE 2022 P2D Q1(f)]
Third generation language (3 GL)
Example: C / Pascal
The codes of third generation lanaguages are more similar to human languages, this makes the codes more readable and easier for programmers to write and maintain
Fourth generation language (4 GL)
Example: SQL (Structured Query Language)
Forth generation language is developed to provide an even higher level of abstraction than third-generation languages
Programmers can write complex programs / write less steps and instructions without worrying about the low-level details of the hardware or software
Fifth generation language (5 GL)
Example: Prolog
Fifth generation languages allow programmers to specify problems in more human language ways and to provide high-level abstractions for complex problem-solving
They are less focused on the syntax of programming and more focused on the problem-solving process (i.e., What to solve)
Evolution of programming languages
Procedural (imperative) programming language
Example: Pascal / C / Fortran
Characteristics
Consists of a main program/a sequence of instructions to be executed in the order designed by the programmer[DSE 2018 P2D Q2(e)] (i.e., Programmers need to specify the details of the logic steps of commands)
It focuses on how a problem can be solved
Easier to trace program logic[DSE 2019 P2D Q3(c)(i)]
Source codes can be written with fewer restrictions[DSE 2019 P2D Q3(c)(i)]
Declarative programming language
Logic e.g., Prolog
Query e.g., SQL
Characteristics
Focuses on what should be solved for a problem
Programmers do not need to specify the algorithm / logic, they just need to state what are required to solve
It focuses on setting the goal (“what to solve”) and the problem is solved by relations (associating facts and rules), but not on specifying how to solve.[DSE 2012 P2D Q4(c)(ii)]
Object-oriented programming language
Example: C# / Python
Characteristics
A program is presented by objects, classes and methods with the use of encapsulation, inheritance, polymorphism [DSE 2018 P2D Q2(e)]
Higher reusability: Because of inheritance, the attributes and methods of new classes can be inherited from the existing classes[DSE 2019 P2D Q3(c)(ii)]
Information hiding: the details of the internal implementation (e.g., how the class/ behaviours is implemented) can be hidden[DSE 2019 P2D Q3(c)(ii)]
Wide range of libraries are provided[DSE 2019 P2D Q3(c)(ii)]
Object-oriented programming
Definition
A program written by object-oriented language is presented by objects, classes and methods with the use of encapsulation, inheritance, polymorphism[DSE 2018 P2D Q2(e)]
Examples of object-oriented languages
Python[DSE 2017 P2D Q3(d)(i)]
C#
C++
Examples of non-object-oriented languages
Fortran[DSE 2017 P2D Q3(d)(i)]
Assembly language
Objects, classes, attributes and methods
What is a class?
It represents the set of attributes(properties) or methods(behaviors) that are common to all objects
Class is the blueprint for an object
Attributes are variables of a program
Methods are functions of a program
Consider the class of a car. Wheels / Speed limits → attributes Increase_speed() / Reduce_speed() → methods
What is a object?
It is the building blocks of object-oriented programs
It is an instance of a class
It contains data values, attributes and methods that are applied to the object
Characteristics of object-oriented programming
Encapsulation
Encapsulation means that attributes and methods are stored in the same object / class
Abstraction
Information hiding: the details of the internal implementation (e.g., how the class/ behaviours is implemented, or the access to certain attributes and methods) can be hidden
Inheritance
Inheritance means that one class can derive or inherit the attributes and methods from other classes
Reusability: the classes can be reused
class can be reused to create different classes through inheritance
shortening the development time
Polymorphism
Methods can be used differently under different situations, but they share the same name
The new method can override the original method
Criteria of selecting programming languages
Scale and modularity
Reusability
Portability Some languages (such as Java and Python) are cross-platform programming language Note: Cross platform languages means that source code can be compiled on different platforms without major changes
Execution efficiency The execution efficiency of C / C++ usually is higher than Python because of more hardware control
Functional strengths Some programming languages (such as SQL) is designed for database, which may not be suitable for developing programs
Readability
Utility libraries and development tools
End-user interaction
Familiarity
Licensing fee for using libraries (other reasonable costs)
Modularity[DSE 2015 P2D Q2(c)(i)]
Definition
System is divided into smaller modules so that each module can be developed by different programmers simultaneously
Reducing development time
Modules can be reused (higher reusability)
Program libraries [DSE 2018 P2D Q2(e)(ii), DSE 2021 P2D Q3(d)(iii)]
Program libraries are external references to other programs
Program libraries usually contain fewer bugs
Providing many suitable, ready-to-use subprograms → It shortens development time
Dynamic link library (DLL)
Saving storage space Since multiple programs can use the same library, and only the references (addresses) are stored in executable codes → this reduces the duplication of codes in the hard disk
