Hi,
I can write your iOS calculator app for you.
I develop apps for iPhone/iPod Touch/iPad running iOS 9 and 8, using Xcode and Swift.
You can see some examples of my work, and client reviews of my completed projects, on my Freelancer profile page (under "portfolio").
It looks like you may be new to Freelancer. Before starting the project, there should be a clear understanding of the details, the deadline, and the milestone payments.
If you'd like to respond to this message, we can discuss things further, before you make your decision on awarding the project.
Best Regards,
- Rob Dixon.