If statement improovement

Projects Programming
1

So i am reading a staemachines last state using EEPROM and reading it. i then want to compare last state and then continue from there. As such i put together a couple of if statements to check which statement is true and execute to enter correct state.

here is a dummy code version

  void setup() {
  Serial.begin(9600);
  unsigned long LastCellNumber = readElapsedTimeCellsFromEEPROM(87); //reading timer value
  unsigned long LastFanNumber = readElapsedTimeFanFromEEPROM(93);   // reading timer value
  int LastState = readStateFromEEPROM(96);                          // Reading stae machine's last state
 
if (LastState == 1) stateMachine.(state1); // Initialise state machine in state 1
if (LastState == 2) stateMachine.(state2); // Initialise state machine in state 2
if (LastState == 3) stateMachine.(state3); // Initialise state machine in state 3
if (LastState == 4) stateMachine.(state4); // Initialise state machine in state 4
if (LastState == 5) stateMachine.(state5); // Initialise state machine in state 5
if (LastState == 6) stateMachine.(state6); // Initialise state machine in state 6
}

Is there a better way to code the if statements i.e do it in less lines or have it do the process quicker? Basically trying to improve my coding knowledge and skills.

2

Hello
you can use the switch/case instruction, too

1 Like
3

Interesting, haven't tried a switch statement before, any chance you know if there are any benefits to using one over the other? if unsure I'll have a browse around.

4

Hello
Generaly I´m using the if-instruction for data flow control and the switch case instruction for state flow control.

5

Thankyou

6

Depending on if/where you add the 'breaks', the switch statement will force the flow through one statement, rather than a set of ifs that could all trigger actions.

You could also use an array to hold the states and have something like stateMachine.states[lastState] and get rid of the ifs/switch altogether

1 Like
7

If state1, state2 etc are functions (nobody knows because you did not provide a complete example), an array of function pointers is the way to go

Below code demonstrates

#define NUM_ELEMENTS(x) (sizeof(x) / sizeof(x[0]))

void state1();
void state2();

void (* stateFunctions [])() =
{
  state1,
  state2,
};

// last state; one based
uint16_t lastState = 2;


void setup()
{
  Serial.begin(57600);
  Serial.print("There are ");
  Serial.print(NUM_ELEMENTS(stateFunctions));
  Serial.println(" state functions");

  //stateFunctions[0]();
  //stateFunctions[1]();

  // hardening to prevent out of bounds
  if (lastState > NUM_ELEMENTS(stateFunctions))
  {
    Serial.println("lastState refers to a non-existing state function");
    for (;;);
  }
  Serial.print("Executing last state (");
  Serial.print(lastState);
  Serial.println(")");

  // hardening to prevent executing a non-specified function
  if (stateFunctions[lastState - 1] == NULL)
  {
    Serial.println("lastState has no function associated with it");
    for (;;);
  }

  stateFunctions[lastState - 1]();

}

void loop()
{
  // put your main code here, to run repeatedly:

}


void state1()
{
  Serial.println("in state1");
}

void state2()
{
  Serial.println("in state2");
}

In your case, it will probably be something like below (without all the hardening)

stateMachine.(stateFunctions[lastState-1]);
8

The string of if statements isn’t really that bad, and it’s easier to debug than a table-driven approach.

9

Hi, I can ask what is this strange (for me) syntax ?
x = stateMachine.(state1);

If statemachine() is a function don't understand the point, if is an object, usally you have a method name after point.

10

yeah, as @sterretje said

11

If you define things right you could use
stateMachine(LastState);
or
stateMachine(States[LastState]);

12

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