Part of the "Chess in C" blog post series. The complete code for part 3.

chessInCPart3-complete.c

#include <stdio.h>
#include <stdlib.h>
#define EMPTY 0
#define KING 1
#define QUEEN 2
#define ROOK 3
#define KNIGHT 4
#define BISHOP 5
#define PAWN 6
#define BREADCRUMB 9

#define POTENTIAL_MOVE_KING 10
#define POTENTIAL_MOVE_QUEEN 20
#define POTENTIAL_MOVE_ROOK 30
#define POTENTIAL_MOVE_KNIGHT 40
#define POTENTIAL_MOVE_BISHOP 50
#define POTENTIAL_MOVE_PAWN 60

int main(void) {
    int board[8][8];
    int i, j;
    int boardValue;

    /* Zero out the board */
    for (i = 0; i <= 7; i++) {
       for (j = 0; j <= 7; j++) {
          /* Zero out the square */
          board[i][j] = 0;
       }
    }

    /* Iterate backward through board
     * The only reason we're iterating backward through the board is to
     * show how smart we are. You don't need to. */
    for (i = 7; i >= 0; i--) {
       for (j = 7; j >= 0; j--) {
          /* Zero out the square */
          board[i][j] = 0;
       }
    }

    /* Set initial start positions */
    /*board[0][0] = ROOK;
    board[0][1] = KNIGHT;
    board[0][2] = BISHOP;
    board[0][3] = QUEEN;
    board[0][4] = KING;
    board[0][5] = BISHOP;
    board[0][6] = KNIGHT;
    board[0][7] = ROOK;
    board[1][0] = PAWN;
    board[1][1] = ROOK;
    board[1][2] = PAWN;
    board[1][3] = PAWN;
    board[1][4] = PAWN;
    board[1][5] = PAWN;
    board[1][6] = ROOK;
    board[1][7] = PAWN;*/

    /* Calculate a rook move */
    /* Variables to store rook position of row 3 and column 4 */
    int pieceRow = 3;
    int pieceColumn = 4;
    board[pieceRow][pieceColumn] = ROOK;

    /* For every row */
    for (i = 0;i <= 7; i++) {
        /* And every column */
        for (j = 0;j <= 7; j++){
            /* ...if the row contains the rook, mark the cell
             * as a possible destination
             * 	(except if the cell contains the piece) */
        	if (i == pieceRow && j != pieceColumn) {
        		board[i][j] = BREADCRUMB;
			}

			/* ...if the column contains the rook, mark the cell
			 *  as a possible destination
			 * 	(except if the cell contains the piece) */
			if (i != pieceRow && j == pieceColumn) {
				board[i][j] = BREADCRUMB;
			}
        }
    }

    /* Print the board */
    /* For every row */
    for (i = 0;i <= 7; i++) {
        /* And every column */
        for (j = 0;j <= 7; j++){
            /* Get the board value */
            boardValue = board[i][j];

            /* And print the contents */
            switch (boardValue) {
              case EMPTY:                   printf(".");
                                            break;
              case KING:                    printf("K");
                                            break;
              case QUEEN:                   printf("Q");
                                            break;
              case ROOK:                    printf("R");
                                            break;
              case KNIGHT:                  printf("N");
                                            break;
              case BISHOP:                  printf("B");
                                            break;
              case PAWN:                    printf("P");
                                            break;
              case POTENTIAL_MOVE_KING:     printf("+");
                                            break;
              case POTENTIAL_MOVE_QUEEN:    printf("+");
                                            break;
              case POTENTIAL_MOVE_ROOK:     printf("+");
                                            break;
              case POTENTIAL_MOVE_KNIGHT:   printf("+");
                                            break;
              case POTENTIAL_MOVE_BISHOP:   printf("+");
                                            break;
              case POTENTIAL_MOVE_PAWN:     printf("+");
                                            break;
              case BREADCRUMB:              printf("+");
                                            break;
            }
          }
          /* At the end of each row, make a new line */
          printf("\n");
     }

    /* Exit the program */
    return EXIT_SUCCESS;
}