Which software is used for developing ios app??

Answer 1

Xcode, Swift, and the iOS SDK. Apple's IDE (Integrated Development Environment) for both Mac and iOS apps is Xcode. It's free and you can download it from from Apple's site. Xcode is the graphical interface you'll use to write apps.
Appery.io, Mobile Roadie, TheAppBuilder, Good Barber,Appy Pie,AppMachine, GameSalad, AppMakr- These are few paid(based on monthly charges) platforms on which you can performs ios development, some if these have multi-language i.e. you can use also for Android and for Web development as well

Answer 2

it is xcode