When converting a 32-bit program to a 64-bit program, only the long and pointer styles change from 32-bits to 64-bits. The integers of type int stay at 32-bits.

Any 32-bit app will refuse to launch and instead show an alert pressuring the developer to release a 64-bit update. Older iPhones and iPads with 32-bit CPUs cannot update to iOS 11 at all.