Why in conditional operator (?:), second and third operands must have the same type?

Question

Why in conditional operator(?:), second and third operands must have the same type?

My code like this:

#include 

        

Answer 1

the ?: expression will produce a value(called rvalue), which is to be assigned to a variable(which is called lvalue), as J.N. metioned, C++ is a statically typed language, lvalue must be known at compile time.

int num = a>b ? a : "eh, string?";

The code above won't compile, cause the variable num can only hold an int, string is not allowed.