How to make cool stuffs like calculator, etc using c++? Please give me example with coding

Answer 1

Collect ideas (from the internet, friends or from yourself)
Think about how you can make your project real.
Take a pen and a sheet of paper and make for example a UML diagramm or think about which class and methods you will need
When you know how to set up the progamm, start coding, it will be simple if you allready solved the problem

Answer 2

Check codeplayground, there are tons of projects with the code aviable.