Update Stacks.cpp to make it input oriented.

[Necron3574]

Fixes #1

Checklist:

• [#] 4 space indentation.
• [#] Coding conventions are followed.
• [#] Input is taken dynamically.
• [#] Sample Input / Output is added at the end of file.
• [#] Logic Documentation (Comments).
• [#] File names are correct.

Make sure these boxes are checked before your pull request (PR) is ready to be reviewed and merged. Thanks!

Changes proposed in this pull request:

• The given stacks program's driver function wasnt input oriented.
• Changed the main function such that the implementation is menu driven.

Languages Used:

• Cpp

Files Added:

• None

We're happy to help you get this ready -- don't be afraid to ask for help.

Thanks!