topic Re: C compiler passing a variable in CodeWarrior for MCU

C compiler passing a variable

DanielMorley — Fri, 29 Dec 2006 00:53:45 GMT

I am using a C compiler to program a MC9S08GT16A

I have the following function

void ReadPosition( int pos){

     if ( POSSW1==DOWN&&POSSW2==DOWN&&POSSW3==DOWN&&POSSW4==DOWN)
       pos=0;

    if ( POSSW1==DOWN&&POSSW2==DOWN&&POSSW3==DOWN&&POSSW4==UP)
     pos=1;

    if ( POSSW1==DOWN&&POSSW2==DOWN&&POSSW3==UP&&POSSW4==DOWN)
      pos=2;

    if ( POSSW1==DOWN&&POSSW2==DOWN&&POSSW3==UP&&POSSW4==UP)
     pos=3;

    if ( POSSW1==DOWN&&POSSW2==UP&&POSSW3==DOWN&&POSSW4==DOWN)
     pos=4;

    if ( POSSW1==DOWN&&POSSW2==UP&&POSSW3==DOWN&&POSSW4==UP)
     pos=5;

    if ( POSSW1==DOWN&&POSSW2==UP&&POSSW3==UP&&POSSW4==DOWN)
     pos=6;

    if ( POSSW1==DOWN&&POSSW2==UP&&POSSW3==UP&&POSSW4==UP)
     pos=7;

    if ( POSSW1==UP&&POSSW2==DOWN&&POSSW3==DOWN&&POSSW4==DOWN)
     pos=8;

    if ( POSSW1==UP&&POSSW2==DOWN&&POSSW3==DOWN&&POSSW4==UP)
     pos=9;

    if ( POSSW1==UP&&POSSW2==DOWN&&POSSW3==UP&&POSSW4==DOWN)
     pos=10;

    if ( POSSW1==UP&&POSSW2==DOWN&&POSSW3==UP&&POSSW4==UP)
     pos=11;


    if ( POSSW1==UP&&POSSW2==UP&&POSSW3==DOWN&&POSSW4==DOWN)
     pos=12;

    if ( POSSW1==UP&&POSSW2==UP&&POSSW3==DOWN&&POSSW4==UP)
     pos=13 ;
    if ( POSSW1==UP&&POSSW2==UP&&POSSW3==UP&&POSSW4==DOWN)
     pos=14;


    if ( POSSW1==UP&&POSSW2==UP&&POSSW3==UP&&POSSW4==UP)
     pos=15;



}

Which works fine. However it does not allow me to pass the pos value back to the main program.

int x;

ReadPosition(x);
   if (x==0){
   Forward();
   Delay(3);
   Brake();
    }

How should I set this up to pass the variable back to the main program

Re: C compiler passing a variable

flashtoo — Fri, 29 Dec 2006 02:29:55 GMT

1) Get a copy of "The C programming Language" by Brian Kernighan and Dennis Ritchie and read it.

2) Create the funciton with a return value not void:

int ReadPosition(int pos) {

// work on pos value and create return value here

pos += 5;

return (pos); // return any variable or constant

}

and call as follows:

int x;

x = ReadPosition(x);
if (x==0){
   Forward();
   Delay(3);
   Brake();
}

Or you could pass "X" as a pointer reference

void ReadPosition(int *pos) {

// work on pos value and create return value here

*pos += 5

return;

}

and call as follows:

int x;

ReadPosition(&x);
if (x==0){
   Forward();
   Delay(3);
   Brake();

}

Bill

Re: C compiler passing a variable

bigmac — Fri, 29 Dec 2006 02:42:29 GMT

Hello Daniel,

Daniel Morley wrote:

void ReadPosition(int pos)
{
   if (POSSW1==DOWN&&POSSW2==DOWN&&POSSW3==DOWN&&POSSW4==DOWN)
      pos=0;

   if (POSSW1==DOWN&&POSSW2==DOWN&&POSSW3==DOWN&&POSSW4==UP)
     pos=1;

   // etc.

}

Which works fine. However it does not allow me to pass the pos value back to the main program.

int x;

ReadPosition(x);
if (x==0) {
   Forward();
  Delay(3);
  Brake();
}

How should I set this up to pass the variable back to the main program

In this case, one method to pass the variable value is to setup pos as a pointer to a variable, and to directly update the variable value from within the function.

void ReadPosition(int *pos)

{
   if (POSSW1==DOWN&&POSSW2==DOWN&&POSSW3==DOWN&&POSSW4==DOWN)
      *pos=0;

   if (POSSW1==DOWN&&POSSW2==DOWN&&POSSW3==DOWN&&POSSW4==UP)
     *pos=1;

// etc.

}

int x;

ReadPosition(&x);
if (x==0) {
   Forward();
  Delay(3);
  Brake();
}

Is this what you are trying to achieve? Alternatively, you could setup the function with a returned int value, i.e. int ReadPosition(void); In this case, pos would be a local int variable within the function.

Regards,

Mac

Re: C compiler passing a variable

DanielMorley — Fri, 29 Dec 2006 02:46:24 GMT

It is working now with the above recommendations being followed. Thanks

Re: C compiler passing a variable

rocco — Fri, 29 Dec 2006 04:52:12 GMT

It is working now with the above recommendations being followed.

You read that book already ! ?

Re: C compiler passing a variable

DanielMorley — Fri, 29 Dec 2006 04:54:38 GMT

in process