C compiler passing a variable

[DanielMorley]

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

[bigmac · Accepted solution]

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

[DanielMorley]

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

[rocco]

---

It is working now with the above recommendations being followed.

---

You read that book already ! ?

[DanielMorley]

in process

[flashtoo]

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