N Queens Problem implemented in C using backtracking technique. Here we have considered n=4. Live Preview : http://codepad.org/FO5V9gk4

NQueens.c

#include<stdio.h>

char a[10][10];
int n = 4;

void printmatrix() {
    int i, j;
    printf("\n");
    for (i = 0; i < n; i++) {
        for (j = 0; j < n; j++)
            printf("%c\t", a[i][j]);
        printf("\n\n");
    }
    printf("-------------------------------------------\n\n");
}

int getmarkedcol(int row) {
    int i, j;
    for (i = 0; i < n; i++)
        if (a[row][i] == 'Q') {
            return (i);
            break;
        }
}

int probable(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 (probable(row, i)) {
                a[row][i] = 'Q';
                nqueen(row + 1);
                a[row][i] = '.';
            }
        }
    } else {
        printmatrix();
    }
}

int main() {
    int i, j;
    for (i = 0; i < n; i++)
        for (j = 0; j < n; j++)
            a[i][j] = '.';
    printf("\nThe solution's are:- \n\n");
    nqueen(0);
    return 0;
}


/*

The solution's are:- 


.	Q	.	.	

.	.	.	Q	

Q	.	.	.	

.	.	Q	.	

---------------------------------------------------


.	.	Q	.	

Q	.	.	.	

.	.	.	Q	

.	Q	.	.	

---------------------------------------------------


*/