What's the usage of char arry?

Answer 1

It depends on what you want to do:
* read a string, put the chars in an array to remove/change them or whatever --> create new string from this array
* put the alphabet in it
* put special characters in it

Answer 2

In what language do you searching the answer? In c the char* (char array) is just a string. In other languages you can use char array for example to generate password from available chars. So array is array, you can use it for many things.