Can we make an app for Android and iOS using a single program?

Question

Why do we have to use different program for making an Android and iOS application and not a single program

Answer 1

Because every programming language has different syntax and set of instructions.

Android, iOS and Windows operating system are also different. That maybe the reason.

Answer 2

because mobile apps call many OS libraries, and it is different in each OS
because Apple or google decide supports only its own choice of programming language for it's mobiles.
but there are some ways how to solve this problem, based on solution of third party