Is this right?

[jjbuchan]

I have the two methods below. In makeBoard am i calling the Boardfill method correctly? I don't really know much about pointers etc.

void Boardfill(Board * B)
{
  int row, col;
  Cell cell;
  for(row=0; row<9; row++) {
      for(col=0; col<9; col++) {
          cell = B->board[row][col];
          cell.visible = ' ';
          cell.npossible = '9';
          int k;
          for(k=1; k<10; k++)
              cell.possible[k] = '1';
      }
  }
}


Board makeBoard(Puzzle p)
{
  Board b;
  
  Boardfill(&b);
  int row, col;
  for(row=0; row<9; row++) {
      for(col=0; col<9; col++) {
          if(p[row][col] == ' ')
              ;
          else
              setvisible(&(b.board[row][col]), p[row][col]);
      }
  }
  return b;
}

 

[columb]

Pointers are the bane of new C programmers - it certainly took me ages to get my head arround them. Start with
Pointers are memory addresses

When I declare

int i;

the program allocates some memory for this. Every time I refer to i I ask the program to return the contents of that memory.

When I declare

 int * ptr = &i;

The program allocates some memory to hold an address and then fills it with the address of i.

So why have pointers?
Reason 1 (in no particular order) When you pass something to a routine that routine gets it's own copy. So if I pass i to a routine and the routine changes it that routine only changes it's copy of i. The original is left unchanged. When you pass a pointer the copy still points to the original and you can make changes to it.
Consider this untested code

#include <stdio.h>

void show_i ( int i )
  {
  i++;
  printf ( "The value of i is %d\n", i );
  }

void show_i_2 ( int * i )
  {
  *i++;
  printf ( "The value of i is %d\n", *i );
  }

main ()
  {
  int i = 1;
  printf ( "first value of i is %d\n", i );
  show_i ( i );
  printf ( "second value of i is %d\n", i );
  show_i_2 ( &i );
  printf ( "third value of i is %d\n", i );
  }

Run this through your compiler and see what happens. show_i changes it's copy of i, not the original. show_i_2 changes the original.

So in your question have you called Boadfill correctly - yes, you have because Boardfill should change the contents of the original board b declared in makeBoard.

Confused - I was and then one day the light came on!

Columb Healy

 

[Diancecht]

I think it's correctly called, but the best wat to know is testing it

A little brief on pointers:

http://www.cplusplus.com/doc/tutorial/pointers.html

Cheers,
Dian