why we can't pass float variable in a switch case in C or C++?

Answer 1

Floats are not exact. There are cases where too different real numbers will be equal when stored as floats. That makes them bad candidates for equality checks like switches.

Answer 2

Because Switch doesn't take that data type.

Answer 3

It's "simple": you could write 0.3333333333333333 and 0.3333333333333331 as two different pattern. But, at compilation time, once floating-point is not precise, both values could result in the same pattern. That means your code is meaningless.