There're different ways to implement a state machine, table-driven, object-driven, function pointer driven, callback based, etc. If you just want a simple and

There're different ways to implement a state machine, table-driven, object-driven, function pointer driven, callback based, etc. If you just want a simple and hard coded sate machine, nothing beats switch statements. You can do something like the following. enum State { S1, S2, S3, S4, ... , END } State transition(State current_state, int input) { switch current_state case S1: switch input case 100: new_state = S3 do_action1() case 101: new_state = S4 do_action2() default: error() case S2: switch input case 100: new_state = S3 do_action3() case 206: new_state = S11 do_action4() case 207: new_state = S12 do_action5() case 208: new_state = S19 do_action6() default: error() case S3: switch input ... ... return new_state } run_state_machine(int[] inputs) { State state = S1 foreach input in inputs state = transition(state, input) } That's it. It's simple to understand and it's clear what the legal transitions are from each state based on the input. You can attach actions and data update on each state transition to do something useful.