Help for a sudoku Solver

I am building a program that can read a sudoku game from file solve it then save it to another file.
The problem is that I can't save the solved sudoku to file altough I have tried.
My code is below...

Code:

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/*Sudoku Solver
 */
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
/* S=3 for standard 9x9 sudoku, I need to find a way to determine the size of the sudoku by reading the input file*/
#define S 2
#define N (S*S)
 
/*  last not included loop*/
#define loop(_I,_From,_To) for (_I=_From;_I<_To;_I++)
 
/*  last included loop */
#define loopto(_I,_From,_To) for (_I=_From;_I<=_To;_I++)
 
#define Error(X) do { fprintf(stderr,"ERROR %s\n",X); exit(1); } while(0)
 
typedef signed char sudoku_t[N][N];
 
 
int valid(int x,int y,int k,sudoku_t s)
/* returns 1 if char k can be put to s[x][y] */
{
  int i,j,x0,y0;
 
  loop (i,0,N) if (s[i][y]==k) return 0;
  loop (j,0,N) if (s[x][j]==k) return 0;
 
  x0=S*(x/S);
  y0=S*(y/S);
  loop (i,x0,x0+S)
    loop (j,y0,y0+S) if (s[i][j]==k) return 0;
 
  return 1;
}
 
void line(char *s)
/* 1 grid line */
{
 
  int i;
 
  loop (i,0,N)
    printf("%c%c%c%c",s[i%S!=0],s[1],s[1],s[1]);
  putchar(s[0]);
 
  putchar('\n');
}
 
void prints(sudoku_t s, char *filename)
/* print sudoku s here is the problem.. need to save solved sudoku to a file  */
{
        /* File pointers to the input file and the outputfile */
    FILE *fp;
  int x,y;
printf("Saving %s...", filename);
 
        // sanity check - game file has to exist and be writable.
if ((fp = fopen(filename,"w")) == NULL) {
                printf("Output file cannot be written!\n");
                return 0;
        }
 
  loop (x,0,N) {
    line(x%S?"| ":"+-");
    loop (y,0,N)
 
      fprintf(fp,"%c %c ",
            y%S?' ':'|',
            s[x][y]?s[x][y]<=9?s[x][y]+'0':s[x][y]+'@':' '); // here is the problem I think... :/
    fputs("|",fp); }
 
  line("+-");
  // write end of line
        fprintf(fp, "\n");
    }
 
    /* Close the output file */
    fclose (fp);
int nsol=0;
 
 
void recursive_search(sudoku_t s)
/*
  scans sudoku for an empty field and tries to put a number 1..N there
  if successfull, calls recursive_search again. h me8odos pou edeikses me xrisi omos ths memcpy
*/
{
  int x,y,k;
 
  loop (x,0,N) loop (y,0,N) {
    if (s[x][y]==0) {
      loopto (k,1,N) if (valid(x,y,k,s)) {
        /* s[x][y]=k is valid, so let's do it and try next */
        sudoku_t news;
 
        memcpy(news,s,sizeof(sudoku_t));
        news[x][y]=k;
        recursive_search(news); }
      /* no digit fits s[x][y], so giving up... */
      return; } }
 
  /* none of s[x][y] is empty ==> we have a solution */
  nsol++; // psaxnw kai gia allo solution an yparxei ;)
}
 
int main(int argc,char **arg)
{
  FILE *fp;
  sudoku_t s;
  int x,y;
  char line[128];
 
  if (argc<2) {
    fprintf(stderr,"No file given!");
    return 0;
  }
 
  else fp=fopen(arg[1],"rt");
 
  if (!fp) Error(arg[1]);
 
  loop (x,0,N) {
    if (!fgets(line,128,fp)) Error("unexpected EOF");
    loop (y,0,N) {
      s[x][y]=line[y]==' '?0:line[y]<='9'?line[y]-'0':line[y]-'@';
      if (s[x][y]<0 || s[x][y]>N) Error("input"); } }
 
  putchar('\n');
 
 
  recursive_search(s);
 
  printf("%d solution%s found\n",nsol,"s"+(nsol==1));
 
  return 0;
}

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That line that seems to be wrong seems awfully cluttered. Ever try unpacking it a little. Maybe then something will spring up...

DO NOT MAKE YOUR OWN LANGUAGE:

Code:

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/*  last not included loop*/
#define loop(_I,_From,_To) for (_I=_From;_I<_To;_I++)

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It generally isn't a good idea to do this.

--
Mats

> here is the problem I think...
Yes, you've been overly cryptic for no good reason.

So ultimately, all you've managed to do is out smart yourself, and now you're stuck.

Try working on the problem and producing some readable code with meaningful variable names, and not something which you can submit to IOCCC.