Difference between user defined and inbuilt functions

 

Aspect	User-Defined Functions	Inbuilt Functions
Definition	Functions that are explicitly written and defined by the programmer to perform specific tasks according to the application's logic.	Predefined functions provided by the programming language or standard libraries to perform commonly required operations.
Availability	Not available by default; must be written by the user in the program.	Available by default and can be used without writing any additional code.
Customization	Fully customizable—users have complete control over the logic, parameters, and behavior.	Not customizable in most cases; their internal implementation is hidden (black box).
Usage Purpose	Created when the program needs specific functionality that is not provided by existing functions.	Used to perform common, repetitive tasks such as mathematical calculations, string manipulations, input/output, etc.
Examples (C Language)	int sum(int a, int b) { return a + b; }	printf(), scanf(), strlen(), sqrt(), etc.
Examples (Python Language)	def greet(name): print("Hello", name)	print(), len(), range(), type(), max(), etc.
Learning Curve	Requires understanding of syntax, parameter passing, return types, and scope.	Easier to use once the names and purposes are known; less effort needed as the implementation is handled internally.
Code Reusability	Encourages modular programming and reuse of custom logic throughout the application.	Enhances efficiency by reducing the need to write code for common tasks.
Performance	Performance depends on the logic and structure written by the programmer.	Highly optimized for performance by the language developers.
Debugging & Maintenance	Easier to debug and maintain because you control the source code.	Errors in using them can be fixed, but internal bugs in the functions themselves are rare and cannot be fixed by the user.
Compilation / Interpretation	Compiled or interpreted as part of the user’s source code.	Part of the language’s runtime or standard library and usually compiled already.
Flexibility	High flexibility in terms of logic, number and type of parameters, return types, etc.	Fixed functionality; only the parameters (if any) can be changed according to documentation.
Dependency	No external dependency unless calling other modules or libraries.	Dependent on language's standard library or imported modules.
Best Use Case	When you need a task-specific logic that is unique to your application and not available as a built-in function.	When performing general-purpose tasks like string manipulation, file handling, mathematics, etc., which are standard in most programs.
Code Portability	May need modifications when moving between different languages or platforms.	Generally portable within programs written in the same language across platforms.
Readability	Can improve readability if functions are well-named and properly documented.	Readable and familiar to most developers; enhances understandability if used appropriately.
Documentation	User is responsible for documenting their own functions for clarity.	Well-documented in language manuals and online references.