C Program to implement 4-Queens Problem using Backtracking

#include<stdio.h>

#include<conio.h>

#include<math.h>

char a[10][10];

int n;

void printmatrix()

{

 int i,j;

 printf("n");

 for(i=0;i < n;i++)

       {

       for(j=0;j < n;j++)

            printf("%ct",a[i][j]);

       printf("nn");

       }

}

int getmarkedcol(int row)

{

       int i,j;

       for(i=0;i < n;i++)

       if(a[row][i]=='Q')

       {

                       return(i);

                       break;

       }

}

int feasible(int row, int col)

{

 int i,tcol;

 for(i=0;i < n;i++)

       {

     tcol=getmarkedcol(i);

           if(col==tcol || abs(row-i)==abs(col-tcol))

              return 0;

       }

       return 1;

}

void nqueen(int row)

{

 int i,j;

 if(row < n)

 {

                for(i=0;i < n;i++)

 {

                                       if(feasible(row,i))

      {

                                                       a[row][i]='Q';

                                                        nqueen(row+1);

                                                       a[row][i]='.';

                                       }

                       }

       }

       else

       {

                       printf("nThe solution is:- ");

                       printmatrix();

       }

}

void main()

{

       int i,j;

       clrscr();

printf("n Enter the no. of queens:- ");

       scanf("%d",&n);

       for(i=0;i < n;i++)

                       for(j=0;j < n;j++)

                                       a[i][j]='.';

       nqueen(0);

       getch();

}