what an api do? code example

Example 1: what is an api

=> On a bare minimum explanation, API are function prototypes which enable the
   user to use the functionality of any component by making a function call 
   without revealing the internal workings of the component.

=> It is a mode of abstraction from the lower layers of software stack , so as 
   to only provide service when needed for higher layers.

=> An API can manifest in many forms, it can be a simple function call in C,
   it can be web service API such as Twitter or FB API, it can be a library call
   to OS kernel, or can be an interrupt routine.


=> API can be just a standalone call or in form of libraries. API are part 
   and parcel of software interaction and data transfer.

Hope this clarifies.

Example 2: what is api

API : Application Programming Interface
An api is a particular set of rules and specifications that programs can 
follow to communicate with each other .
The end user sends request , API executes instructions then get the data 
from the server and responds to the user.