Thread: 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.

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.

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.

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.