C largest unsigned int

Type	 			Storage size						Value range
signed char				1 byte							-128 to 127
int						2 byte						-32,768 to 32,767
int						4 bytes	 		 		-2,147,483,648 to 2,147,483,647
unsigned int			2 bytes						   0 to 65,535 
unsigned int			4 bytes						 0 to 4,294,967,295
short					2 bytes						-32,768 to 32,767The sizeof function will help you here.
  sizeof(data type) returns a size_t //Number of bytes whatever the input for sizeof takes

Example:
//This statement will return 2 or 4 (depending on your system)
  return sizeof(int)