Homepage(german)     Computer stuff(german) [deutsch]     [français]

# The 8 Queens Puzzle

This is an old puzzle and a popular homework in programming courses. The problem is to place 8 queens on a chessboard, so that no queen is beaten by another. Here is a rather small C-program, which finds all solutions. It contains about 45 lines of code (inclusively comments), but 1/3 are for the output.

 ```+----------------+ | <> | | <> | | <> | |<> | | <>| | <> | | <> | | <> | +----------------+ ```

It is an ANSI-C program with an ascii-output. So it should run on all operating sytems an should compile with all C-compilers.

Download: damen.c (7747Byte) [The stripped code is 3,5K.]

Here is the program for inspection.

```#include <stdio.h>
#include <stdlib.h>

int x; /* x[i] = x coordinate of queen in row i. */

/* prints field */
void print ()
{
int i,j;
printf ("+----------------+\n");
for (i=0; i<8; i++) {
printf ("|");
for (j=0; j<8; j++)
if (j==x[i]) printf ("<>");
else printf ("  ");
printf ("|\n");
}
printf ("+----------------+\n\n");
}

/* tests, whether (ix, iy) is beaten by queens 0...(iy-1) */
int is_free (int ix, int iy)
{
int i;
for (i=0; i<iy; i++)
if ((x[i]==ix) || (abs(x[i]-ix)==abs(i-iy))) return 0;
return 1;
}

/* tries to place queen n on row n */
void try (int n)
{
int i;
if (n==8) print();
else
for (i=0; i<8; i++)
if (is_free(i,n)) {
x[n]=i;
try (n+1);
}
}

int main ()
{
try (0);
return 0;
}

```

 Homepage(german)     Computer stuff(german) by Michael Becker, 2/2002. Last modification 4/2003