Question

which device in computer uses to find index number

Answer 1

I don't know about device but i know a code to find index of an array or variable with string datatype and it is
<arrayname>/<variablename>.indexOf ('<character>');

note: the above code is of Java

Answer 2

I don't think about gadget yet I know a code to discover record of an exhibit or variable with string datatype and it is <arrayname>/<variablename>.indexOf ('<character>'); take note of: the above code is of Java.

If Index is an interesting distinguishing number related with a physical or coherent interface. For most programming, the if Index is the name of the interface.