why use API code example

Example 1: what is an api

An application program interface (API) is a set of routines, protocols, and
tools for building software applications.

Basically, an API specifies how software components should interact.
Additionally, APIs are used when programming graphical user interface (GUI)
components.

A good API makes it easier to develop a program by providing all the
building blocks. A programmer then puts the blocks together.

Example 2: purpose of api

Knowing the purpose of the API will
set a firm foundation for you to
well prepare your test data for input
and output. This step also helps you
define the verification approach.
For example, for some APIs, you will
verify the responses against the
database; and for some others, it is
better to verify the responses 
against other APIs.