validate and new feature

[nishant23122000]

As per me we have to check whether number is valid or not which are passes in arguments in calculator section.
and we can add more operations like power,modules etc .

Here is the validation code which i done :

Also i optimize the index.js with adding commands.js . so it's easy to understand clearly

please check this and assign this issue to me because i already did it

[Mukulbaid63]

@nishant23122000 go on man