Application Programming Interface (API) introduction

An API is a way for two or more software components to communicate with each other. APIs define rules for how requests and responses should be structured.

Types

There are different types of APIs depending on how they are used and what they interact with:

API Type	Description	Example
Local APIs (OS APIs)	These allow applications to interact with the operating system.	Win32 API → Used for Windows applications to interact with system resources like files, memory, processes, etc. Which provides functions like CreateFile(), ReadFile(), etc., which allow programs to access the Windows system.
Web APIs	These allow communication over a network, often using HTTP.	REST API, SOAP API, GraphQL API, A client sends a request (e.g., GET /users) to a server, and the server responds with data.
Library APIs	These APIs are built into software libraries to allow developers to use pre-built functionality.	The .NET API (like System.IO.File.ReadAllText()) lets you work with files in C#.
Hardware APIs	These allow software to communicate with hardware.	Example: DirectX API → Used in game development to interact with GPUs.