1. Using enum

2. Define some system values
//Define some states for an I/O device, such as a disk drive
// O/S needs to test to see what state it is in
Enum IO_status //These are the ONLY values allowed
{UnInitialized,
Initialized,
Ready,
Started,
Inprogress,
Completed,
Busy,
Error,
Sense_data_pending }

3. Now use those values
int IO_test(const IO_Status disk_state) // only enum values are legal { // cannot assign an arbitrary value to a name switch(disk_state) { case UnInitialized: Initialize_disk(disk_id); return(0); case Busy: return(-1); case Sense_data_pending: Get_sense_date(disk_id); //Put it where caller can get it Return(sense_error); // etc. Default: return (-1); }

4. Issues No type-checking (can be signed /unsigned)
Cannot print the "name" of the value ("Busy") cout<<busy; // yields an integer a table lookup would be needed
Alternative: use a string.
Can't use a switch
Case sensitivity
Compare is slower
Uses more memory
Can print the name