# C > Beginners Lab Assignments Code Examples

## N-Queen's Problem

``` N-Queen's Problem #include <iostream.h> #include <ctype.h> #include <stdlib.h> #include <stdio.h> #include <conio.h> void check(int, int, char [100][100]); void print(char [100][100]); int no_of_queens, queen = 2, flagrow = 0, flagcol = 0; int count = 1; char ch, response_row, response_col; int main(void) { int row, col, i; char board[100][100], response; clrscr(); printf(" @@ This is n-queen problem. Enter the number of queens(say n) and watch how computer places them in (n x n) matrix such that none can meet another moving along horizontally, vertically or digonally. "); printf(" Enter the number of queens : "); scanf("%d", &no_of_queens); if(no_of_queens > 23) { printf(" @@ Thought the program is OK for any queen value.But due the configuration of the output screen the output will be tranketed (A very large queen number may cause the system stack overflow). So it is highly recommended that you run the program with maximum queen number 23..."); printf(" Want to continue(Y/N)?"); fflush(stdin); scanf("%c", &response); if(toupper(response) == 'N') return (0); } else if(no_of_queens < 3) { printf("The number of Queen must be greater than 3."); getch(); return (0); } printf("Want a row number below the board(Y/N) : "); fflush(stdin); response_row = (char)getchar(); if(toupper(response_row) == 'Y') flagrow = 1; printf("Want a column number below the board(Y/N) : "); fflush(stdin); response_col = (char)getchar(); if(toupper(response_col) == 'Y') flagcol = 1; clrscr(); printf("M/c in work ! Please Wait..."); // This for-loop is used for checking all the columns of row 0 only... _setcursortype(_NOCURSOR); for(col = 0; col < no_of_queens; col++) { memset(board, '-', sizeof(board)); check( 0, col, board ); } clrscr(); printf("Thank you for seeing this program through."); getch(); return (0); } void check( int r, int c, char board[100][100] ) { int i, j; // Terminating condition for the recursion... if ( ( r == no_of_queens ) && ( c == 0 )) { clrscr(); printf(" (%d-Queen) Set : %d ", no_of_queens, count++); print( board ); fflush(stdin); ch = (char)getch(); clrscr(); if(ch == 'e') exit (0); printf("M/c in work ! Please Wait..."); } // Vertical check... for(i = 0; i < r; i++) { if ( board[i][c] == queen) return; } // Horizontal check... for(j = 0; j < c; j++) { if ( board[r][j] == queen) return; } // Left-Diagonal check... i = r; j = c; do { if ( board[i][j] == queen ) return; i--; j--; } while( i >= 0 && j >= 0 ); // Right-Diagonal check... i = r; j = c; do { if ( board[i][j] == queen ) return; i--; j++; } while( i >= 0 && j < no_of_queens ); // Placing the queen if the ckecked position is OK... board[r][c] = queen; r++; // This for-loop is used for checking all the columns for each row //starting from 1 upto the end... for(int p = 0; p < no_of_queens; p++) check(r, p, board); for(int h = 0; h < no_of_queens; h++) board[r - 1][h] = '-'; } void print(char board[100][100]) { for(int i = 0; i < no_of_queens; i++) { if(flagrow == 1) printf("%3d", i + 1); for(int j = 0; j < no_of_queens; j++) { if(board[i][j] == queen) { textcolor(RED); cprintf("%3c", queen); } else { textcolor(8); //dark gray cprintf("%3c", 22); } } printf(" "); } textcolor(7); if(flagcol == 1) { if(flagrow) printf(" "); for(i = 0; i < no_of_queens; i++) printf("%3d", i + 1); } gotoxy(62, 1); printf("Press E to exit."); textcolor(7); } ```