Calling subroutines

[tb0508]

I am writing with an arduino but I have a basic question dealing with subroutines.

I have 3 subroutines, and two of them calculate a value. I want to send both of the subroutine values to one subroutine to do another calculation and was wondering how to do that. Here is an example of what I am trying to do.

I am wanting to send 'targetPos' and 'currentPos' to the calculateError to do a calculation with both values. Not sure how to call them. Or would I just need to use both of those values and do the calculation inside main(or void loop in the arduinos case)?

void pSteer (const unsigned int value)
{
  
  int steering = constrain(value, 400, 1023);
  
   int targetPos = map(steering, 400, 1023, -100, 100);

   calculateError(targetPos);
  
} 

void pWheel(const unsigned int value)
{

  int wheel = constrain(value, 150, 480); 
  
  int currentPos = map(wheelInput, 150, 480, -100,100);

  calculateError(currentPos);
}

void calculateError(.........)
{
   int error = targetPos - currentPos;
}

[claudiu]

Well presumably the function that you are sending the values to takes two parameters of the types of your "calculations". Then you can just call that function with your two values as arguments.

i.e. calculateError(currentPos,targetPos);

[tb0508]

Ok, I am trying to and am getting an error.

"variable or field 'calculateError' declared void"
Trying implementing it like:
void calculateError(targetPos,currentPos) and
calculateError(targetPos, currentPos)

[claudiu]

well that's because you haven't specified the type of the parameters in your function prototype.

[tb0508]

I did not just did not mention it, gave me an error like:
"to few arguments to 'void calculateError'"

Yes, I am sure I am missing something but just not sure what.

[rogster001]

Too few arguments means you have not supplied the correct number of arguments to your function.

if you declare:

void MyFunction(int i, int j)
{

  //...

}

And then call:

MyFunction(i);

Then you have supplied too few arguments

[tb0508]

This compiles but not sure if it is correct for what I want. I am wanting to take the values I have gotten 'targetPos' and 'currentPos' in the previous subroutines and use them in calculateError. Will I have to make a call from main with this? Not sure if this will use those specific values or will want to be call the subroutine from main with two arguments.

void pSteer (const unsigned int value)
{
   
  int steering = constrain(value, 400, 1023);
   
   int targetPos = map(steering, 400, 1023, -100, 100);
 
   //calculateError(targetPos);

   
} 
 
void pWheel(const unsigned int value)
{
 
  int wheel = constrain(value, 150, 480); 
   
  int currentPos = map(wheelInput, 150, 480, -100,100);
 
  //calculateError(currentPos);

}
 
void calculateError(int currentPos, int targetPos)

{
   int error = targetPos - currentPos;
}

[rogster001]

At the moment targetPos and currentPos are local to the functions you have delcared them in, they will not exist after the curly braces in each of those functions.

You need to show a bit more code perhaps to clarify what your aim is, at present whatever you are trying won't work because target and current exist seperately from one another.

You understand? At it is, As soon as pSteer() completes then targetPos has gone. And likewise in pWheel() and currentPos

[claudiu]

You should have those two functions "return" what you want, and use those values as arguments for your other function.

[tb0508]

At the moment targetPos and currentPos are local to the functions you have delcared them in, they will not exist after the curly braces in each of those functions.

You need to show a bit more code perhaps to clarify what your aim is, at present whatever you are trying won't work because target and current exist seperately from one another.

You understand? At it is, As soon as pSteer() completes then targetPos has gone. And likewise in pWheel() and currentPos

Yea, that is what I understand. My problem is trying to use targetPos and currentPos before they are gone. Maybe claudiu explained it with the return.

You should have those two functions "return" what you want, and use those values as arguments for your other function.

Ok, so changed the code a little to return the value and call the calculateError function again.

int pSteer (const unsigned int value)

{
    
  int steering = constrain(value, 400, 1023);
    
   int targetPos = map(steering, 400, 1023, -100, 100);
  
   //calculateError(targetPos);
   return targetPos;


 
    
} 
  
void pWheel(const unsigned int value)
{
  
  int wheel = constrain(value, 150, 480); 
    
  int currentPos = map(wheelInput, 150, 480, -100,100);
  
  //calculateError(currentPos);
  return currentPos;


 
}
  
void calculateError(int currentPos, int targetPos)
 
{
   int error = targetPos - currentPos;
}

void loop() //This is the main
{
  //calculateError(targetPos,currentPos); //error when this is used, guess it is wrong.
}

[claudiu]

That's because targetPos and currentPos don't exist outside the scope of their functions. You have to call the functions and pass their return values as arguments to calculateError.