Assigning an integer value into a floating-point variable is like putting a small object into a large box. The int type goes up to approximately 2 billion. Its easy to fi t 2 billion into a double box because a double goes all the way up to 1.8 10 308 . On the other hand, assigning a floating-point value into an integer variable is like putting a large object into a small box. By default, thats illegal.