is there an if/else function that implements IMMEDIATELY?

I'm in the middle of righting a program for a servo motor. I'd like to use an if and else to have the motor exit the main program with a pin going low and I'd like it to do it immediately.

Right now I have it as an

Code:

---

if ...
{
whole bunch of for loops.....
...
...
...
}

else...
{
single command.
}

---

and it's working but the problem is that it doesn't exit out of the if statement's code immediately and that's what I'm after. Right now it's running the code in the if statement from start to finish. I'd rather have it jump to the else immediately and NOT finish the if's code.


Is there a good way to pull that off?

You probably want a goto.


Quzah.

One thing I didn't think of....

while loop

Would that do what I'm thinking?

If you want an immediate response you need to get your pin test inside the loops. Depending on the parts of the code you didn't show us a while() or do while() may work for you...

You either need to do a whole bunch of this:

Code:

---

while( ... && !BAILOUT )
{
    while( ... && !BAILOUT )
    {
        while( ... && !BAILOUT )
        ...
        if( BAILOUT ) break;
    }
    if( BAILOUT ) break;
}

---

Or you just goto BAILOUT; from wherever you need to.


Quzah.

What about a while loop wrapping that one, important, if?

Code:

---

. . .
while (expected common condition exists) {

if Previous-Important-If (test) {

Response

Response

}

/*  Ending the while loop which holds the important IF */

}

Other, less important IFs, from the long sequence of IFs before  . . .

---

Examples of this would be in K&R's C in Chapter 1. There were a bunch of getchar/putchar examples with counting and reporting and replacement that used this in the book.

Here's what I've got as the main bones of my code. I tried the Goto and bailout and it isn't working for some reason. It is not entering the while loop until the condition is met but once it's in, it doesn't leave.

Code:

---


void setup()
{
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object
  pinMode(relaypin, INPUT);
}
 

void loop()  // Program begins here. 
{
  // read the state of the relay value (checks pin 2 for 5V to see if winder motor is on) 
  relaystate=digitalRead(relaypin);


while (relaystate == HIGH)
{
// if Relay for the motor is high (5V) then run the pickup program)
 
if (relaystate == LOW){ goto bailout;}





  for(pos = (minimum-p*1.3); pos >= maximum+p; pos -= posinc) 
  {                                 
    myservo.write(pos);           
    delay(4);                     
  }
 
  for(pos = maximum+p; pos<(minimum-p*1.3); pos+= posinc)  /// moving from right to left (i.e. 9 to 146 degrees)
  {                               
    myservo.write(pos);         
    delay(4);                     
  }
}

}



  for(pos = 75; pos < slowleft; pos+=1) 
  {                               
    myservo.write(pos);         
    delay(23);                     
  }// transition


}

bailout:
 pos = slowleft; pos+=1; 
                                 
    myservo.write(pos);         
    delay(23);                     
  // goes to slowleft (left side of the pickup) if the winder motor is off.

}

---

What the hell is going on with the curly braces? Your indentation has you completely screwed up I think. Or at least it has me all screwed up.

It looks like your loop() function ends shortly (3 braces) after the delay(4); statement and all the code after that is in non-function limbo land.

Maybe re-indent your code in a sane way and you'll be able to see what's really going on.

Your indentation is terrible.

Code:

---

void loop()  // Program begins here. 
{
    // read the state of the relay value (checks pin 2 for 5V to see if winder motor is on) 
    relaystate=digitalRead(relaypin);

    while (relaystate == HIGH)
    {
        // if Relay for the motor is high (5V) then run the pickup program)
        if (relaystate == LOW){ goto bailout;}

        for(pos = (minimum-p*1.3); pos >= maximum+p; pos -= posinc) 
        {                                 
            myservo.write(pos);           
            delay(4);                     
        }
 
        for(pos = maximum+p; pos<(minimum-p*1.3); pos+= posinc)  /// moving from right to left (i.e. 9 to 146 degrees)
        {                               
            myservo.write(pos);         
            delay(4);                     
        }
    }
}
What's all this?
  for(pos = 75; pos < slowleft; pos+=1) 
  {                               
    myservo.write(pos);         
    delay(23);                     
  }// transition

}

bailout:
 pos = slowleft; pos+=1; 
                                 
    myservo.write(pos);         
    delay(23);                     
  // goes to slowleft (left side of the pickup) if the winder motor is off.

}

---

It doesn't reach your goto because it's not in any actual block of code. But, since you're only exiting one loop anyway, why don't you just break?


Quzah.

That's not all of my code. It's pretty long so the braces may not all add up properly. I cut out most of the code just to give the idea.

I'm sure the indentation is horrible. It's a result of a bunch of cut and pastes. The main program is doing what I need it to so far.


by the way I'm not a programmer... I'm a wannabe who's a EE. I got a C in my C++ course. I'm definitely a hack. This is my first real crack at a program I've cared about. Cleaning up will be important if I do this again!

Quote:

---

Originally Posted by quzah

You either need to do a whole bunch of this:

Code:

---

while( ... && !BAILOUT )
{
    while( ... && !BAILOUT )
    {
        while( ... && !BAILOUT )
        ...
        if( BAILOUT ) break;
    }
    if( BAILOUT ) break;
}

---

Or you just goto BAILOUT; from wherever you need to.


Quzah.

---

goto is pretty much a last resort these days.
There are so many other ways of exiting loops it should never be necessary...
I think most would agree it's to be avoided.

Anyone have an example of how I would do this with a while?

My digital input trigger to start the while loop is working but it's going into the loop and never exiting. I guess that means (based on what you guys have said) that it's not reading while the loop is running.

Quote:

---

Originally Posted by CommonTater

goto is pretty much a last resort these days.
There are so many other ways of exiting loops it should never be necessary...
I think most would agree it's to be avoided.

---

/golfclap

He specifically mentioned a "whole bunch of for loops". If you want a simple way to get out of a bunch of nested loops in a single jump, a goto is the clearest option. Otherwise, if they're not nested, then he just needs to wrap them all in a single check, as we've already said.


Quzah.

> by the way I'm not a programmer... I'm a wannabe who's a EE
Then you must have heard of state machines right?

Some pseudo code

Code:

---

state = RUNNING;
while ( state != DONE ) {
  if ( digitalRead(relaypin) )
    state = BAILOUT
  switch ( state )
    case MOVE_LEFT
      // bump motor one step left
      // if goal reached, state = MOVE_RIGHT
    case MOVE_RIGHT
      // bump motor one step right
      // if goal reached, state = DONE
    case BAILOUT
      // bump motor one step wherever
      // if goal reached, state = DONE
    // end case
  delay()
}

---

The code doesn't "get stuck" in some deeply nested loop. There is just one loop with a state, and you decide what to do in each state, and when to move to a new state.


> it doesn't leave

Code:

---

  relaystate=digitalRead(relaypin);


while (relaystate == HIGH)
{
// if Relay for the motor is high (5V) then run the pickup program)
 
if (relaystate == LOW){ goto bailout;}

---

It doesn't leave because you never call digitalRead(relaypin); inside the loop.

Ok, now I have it in the while loop:

Code:

---


while (relaystate == HIGH)
{
// if Relay for the motor is high (5V) then run the pickup program)
 
   
 pinMode(relaypin, INPUT);
  // read the state of the relay value (checks pin 2 for 5V to see if winder motor is on) 
  relaystate=digitalRead(relaypin);

....

---

Did this now and it will not start until it gets the HIGH signal but still runs through the entire while loop before stopping. I am really stuck on how to get it to exit the while loop with a realtime reading of the pin as it goes LOW.

If your MCU supports interrupts; I would place the call to the function in the interrupt service routine.

Tim S.

Quote:

---

Originally Posted by 777funk

Did this now and it will not start until it gets the HIGH signal but still runs through the entire while loop before stopping. I am really stuck on how to get it to exit the while loop with a realtime reading of the pin as it goes LOW.

---

It only enters the loop while the condition is true. If it's not true when it reaches the loop the first time, it's going to skip it completely. If you need it to execute at least once, use a do-while. Or, put what always has to happen first outside the loop, and then if it needs to be inside too, put it there too.


Quzah.

Well I actually don't necessarily want it to execute all the way through any of the sub loops (and their are lots of them within the main while loop which is triggered by the HIGH pin) in my program even once. I just want it to operate like a switch... as soon as I tell it to stop, I want it to stop and exit the loop in the program.

So far GOTO, Break, and everything else suggested works but it doesn't immediately get out. It finishes the sub loop it's currently in and THEN exits. That's not quite what I'm looking for.

I want the program to drop what it's doing and exit the main while loop that houses the other loops within the program.

Any pointers on that?