Hello, can somebody explain the difference between cast and conversion, please?
The "conversion" is creating a float from the value in the parentheses. Since you have not given x a value, you haven't a clue what will be in y.
The cast is telling the compiler to treat some number of bytes (4 in the case of a float cast) as though they were a float. The first byte is the first byte of the variable x. The second byte is the second half of x. The 3rd and 4th bytes are whatever bytes follow x in memory.
The result of that cast will be garbage in y, too.