What is the iOS :: app in C?

It’s a tough superset of C which makes any C code a valid Objective-C program. Even though Swift is now the suggested language for developing iOS apps, there are still good reasons to use past languages like C, C++ and Objective-C.

Can I make iOS app with C?

About XCode, Swift, and Objective-C

Included with XCode is support for Apple’s newer Swift programming language, made specifically for iOS and macOS. While Apple is pushing Swift, you can also program iOS in Objective-C.