Thread: Reading an array and displaying the outcome using a look up table in C

Originally Posted by algorism

I don't recall saying the loop should go before main. That makes no sense.

The OP is referring to the function declaration. Changing the return type of "pattern" is producing errors, so I suggested they make sure the function is prototyped.

Originally Posted by algorism

Your pattern function still isn't returning anything.

I don't understand your PORTB question. Looks like you're assigning to *PORTB in the loop.

As stated above, this was apparently causing errors. I'm not sure why, though, based on the code.

@OP: See an example of declaring a function (before main) when defining it after main: function calsum should have a prototype??

If this is causing errors, post the updated code along with the error messages.

not sure why the code is going like that

Originally Posted by owenb11

not sure why the code is going like that

Try it again. It's not readable like that.
Make sure you copy and paste it as plain text.

Originally Posted by owenb11

not sure why the code is going like that

Well, try again. Apart from being unreadable, I think most of it didn't make it to the forum. Go to the advanced page, paste as text, and preview the post to ensure the code is formatted correctly.

Originally Posted by Matticus

Well, try again. Apart from being unreadable, I think most of it didn't make it to the forum. Go to the advanced page, paste as text, and preview the post to ensure the code is formatted correctly.

Ok here goes again

Code:

#include <stdio.h> 
unsigned char pattern (int); // set up function //
 int main(void){
   
/******************* Declare the port addresses **********************/    
unsigned char *DDRA  = (unsigned char *)0x0002;    
unsigned char *PORTB = (unsigned char *)0x0001;    
unsigned char *DDRB  = (unsigned char *)0x0003;   
 unsigned char *PTH   = (unsigned char *)0x0260;    
unsigned char *DDRH  = (unsigned char *)0x0262;  
  unsigned char *PERH  = (unsigned char *)0x0264;   

  /******************* Declare variables *******************************/    
unsigned char threshold;   
 unsigned char index;    
unsigned char i;    

 /******************* Declare function prototypes**********************/  

  void wait(int); //set up of function //   

   /************************** Scanner Data ******************************/     

unsigned char scanner[ 255 ] = { 50,           
     4,  9, 14, 18, 23, 26, 29, 30, 31, 32, 
  34, 37, 41, 47, 54, 63, 71, 80, 87, 92,                                  
   94, 94, 92, 89, 85, 83, 83, 86, 93,102,   
   115,128,141,153,161,164,164,160,152,144,          
 137,132,132,136,146,161,178,196,213,226                                   };     

/******************* Set up I/O ports ********************************/    

*DDRH = 0x00;                   /* make Port H an input port */  

  *PERH = 0xFF;                   /* enable Port H */    

*DDRA = 0xFF;                   /* make Port A an output port */   

 *DDRB = 0xFF;                   /* make Port B an output port */   

  /******************* Main loop ***************************************/     
 
 *PORTB = 255; // This clears the display on PORTB //  
    
 threshold = *PTH; // Make threshold equal to *PTH //   
 
   index = 1;      

 for ( i = 1; i <= scanner[0] && scanner [i] < threshold; i++)     

  {         

 *PORTB = pattern (scanner[i]/32);         

    wait (1);   

   }     

   if ((index < threshold))   

    {      

 printf("threshold reached at reading %d with a current value %

d." ,index ,scanner[index] );    
   }   
    else    
   {     
  printf (" Threshold not reached after %d readings." ,scanner[0]);       }     
  return 0 ;   
   }   
/******************* Pattern Function **********************************/   
    unsigned char pattern (char sw_data)   
    {          
  unsigned char LedTable [8] = { 0b00000001, 0b00000011, 

0b00000111, 0b00001111,                                         

  0b00011111, 0b00111111, 0b01111111, 0b11111111 };   

 
        unsigned char data;         
   unsigned char display;        
    unsigned char sw_on;         
   unsigned char sw_off;         
 
   data = sw_data;          

  sw_on = ((unsigned char) LedTable[data]);  

          sw_off = sw_data & 0b11111111;     

     if  ( sw_off & 0b00010000)          
   {          
  display = sw_on | 0b10000000 ;      
      }     
    else          
  {          
  display = sw_on & 0b01111111;       
     }      
    }  

 /********************** Wait Function **********************************/    
 void wait (int seconds)    
 {    
unsigned int i;  
  unsigned int j;  
  unsigned int k;     

  for ( k = 0; k <= seconds; k++)    

  {      

 for ( i = 0; i <= 50; i++) 

     {    
   for (j =0; j <= 2000; j++); 
     }   
   } 
   }

So the error message is conflicting types for pattern and leads me to both times pattern is declared.

Function declaration:

Code:

unsigned char pattern (int);

Function defintion:

Code:

unsigned char pattern (char sw_data)
{
    ...

Something isn't lining up correctly.

Duh! don't know how I missed that one! that's the error cleared.

As for my pattern function not returning anything I really do not know where to go from where I am....?

You return a value from the function. The link I posted above includes a return statement for illustration.

Think about it with an analogy. Here was the original version of the function:

Code:

void pattern (char threshold)

It expects a character, but does not return anything (void). It's like a parking meter - you put money into it (pass it a char), but you get nothing tangible back (void).

Now look at the updated version:

Code:

unsigned char pattern (char sw_data)

It expects a character, and returns an unsigned character. It's like a vending machine - you put money into it (pass it a char), and it returns a candy bar (unsigned char).

Speaking of which, you should make that function argument unsigned.

That's cleared things up thanks!