loop not incrementing correctly

Hello, so I have been working on a program that will eventually allow you to play connect four. As of now I am still worknig on the basic functions: playing a move, testing if the move wins and etc. my current code is this:

Code:

#include <iostream>
#include <vector>
using namespace std;

const short BOARDX = 7;
const short BOARDY = 6;

void output_board();
short play_move(short x, short player); //0 = fail 1 = succeed 2 = game won
bool test_win(short x, short y);
bool test_v(short x, short y);
bool test_h(short x, short y);
bool test_d(short x, short y);


vector<vector<char> > board(BOARDX, vector<char>(BOARDY));

int main()
{
    cout << "Hello, this is a bare bones rendering of the connect four game." << endl;
    for(short a = BOARDY; a >= 0; a--) //for testing
    {
      cout << play_move(a,1) << endl;
      output_board();
    }

    return 0;
}

void output_board()
{
  for(short y = BOARDY - 1; y >= 0; y--)
    {
      for(short x = 0; x < BOARDX; x++)
      {
        cout << "|";
        switch (board[x][y])
        {
          case 0:
            cout << " ";
            break;
          case 1:
            cout << "X";
            break;
          case 2:
            cout << "O";
            break;
          default:
            cout << "E";
            break;
        }
      }
      cout << "|" << endl;
    }
  return;
}

short play_move(short x, short player)
{
  //starting from the bottom, selects the bottom unoccupied space and puts the player there
  //returns 2 if the game is won, 1 if it is successful, and 0 if the column is filled
  for(short y = 0; y < BOARDY; y++)
  {
    if(!board[x][y])
    {
      board[x][y] = player;
      if(test_win(x, y))
        return 2;
      return 1;
    }
  }
  return 0;
}

bool test_win(short x, short y)
{
  //test the entered location for a win
  if(board[x][y])
  {
    if(test_h(x, y))
      return 1;
    if(test_v(x, y))
      return 1;
    if(test_d(x, y))
      return 1;
  }
  return 0;
}

bool test_v(short x, short y)
{
  //test verticals
  short line_length = 1;
  for(short x_down = x - 1; x_down >= 0 && board[x][y] == board[x_down][y]; x_down--)
    line_length++;
  if(line_length >= 4)
    return 1;
  return 0;
}

bool test_h(short x, short y)
{
  //test horizontals, right is currently not working
  short line_length = 1;
  for(short y_right = y + 1; y_right < BOARDY && board[x][y] == board[x][y_right]; y_right++)
    cout << line_length++ << endl;// cout for testing
  for(short y_left = y - 1; y_left >= 0 && board[x][y] == board[x][y_left]; y_left--)
    line_length++;
  if(line_length >= 4)
    return 1;
  return 0;
}

bool test_d(short x, short y)
{
  //test for diagonals with a positive slope
  short line_length = 1;
  short x_positive = x + 1;
  short x_negative = x - 1;
  short y_positive = y + 1;
  short y_negative = y - 1;
  for(; x_positive < BOARDX && y_positive < BOARDY && board[x][y] == board[x_positive][y_positive]; x_positive++ * y_positive++)
    line_length++;
  for(; x_negative >= 0 && y_negative >= 0 && board[x][y] == board[x_negative][y_negative]; x_negative-- * y_negative--)
    line_length++;
  if(line_length >= 4)
    return 1;
  // now test for diagonals with a negative slope
  line_length = 1;
  x_positive = x + 1;
  x_negative = x - 1;
  y_positive = y + 1;
  y_negative = y - 1;
  for(; x_positive < BOARDX && y_negative >= 0 && board[x][y] == board[x_positive][y_negative]; x_positive++ * y_negative--)
    line_length++;
  for(; x_negative >= 0 && y_positive < BOARDY && board[x][y] == board[x_negative][y_positive]; x_negative-- * y_positive++)
    line_length++;
  if(line_length >= 4)
    return 1;
  return 0;
}

When run,Ii get this output:

Code:

Hello, this is a bare bones rendering of the connect four game.
1
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | |X|
1
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | |X|X|
1
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | |X|X|X|
1
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | |X|X|X|X|
1
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | |X|X|X|X|X|
1
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| |X|X|X|X|X|X|
1
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
|X|X|X|X|X|X|X|

Process returned 0 (0x0)   execution time : 0.109 s
Press any key to continue.

The problem I am having is, test_h does not appear to check to the right. which is done by this line:

Code:

for(short y_right = y + 1; y_right < BOARDY && board[x][y] == board[x][y_right]; y_right++)
    cout << line_length++ << endl;

For whatever reason, this does not add to line_length, but the other half of test_h works fine. I have asked my teacher about this, rewritten the line 3 times and for the life of me I cannot figure out what is wrong.

Have you got vertical and horizontal mixed up?

Code:

(gdb) break test_h
Breakpoint 1 at 0x401047: file bar.cpp, line 98.
(gdb) run
Starting program: /home/sc/Documents/a.out 
Hello, this is a bare bones rendering of the connect four game.

Breakpoint 1, test_h (x=6, y=0) at bar.cpp:98
98	  short line_length = 1;
(gdb) cont
Continuing.
1
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | |X|

Breakpoint 1, test_h (x=5, y=0) at bar.cpp:98
98	  short line_length = 1;
(gdb) cont
Continuing.
1
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | | | |
| | | | | |X|X|

Breakpoint 1, test_h (x=4, y=0) at bar.cpp:98
98	  short line_length = 1;
(gdb) s
99	  for (short y_right = y + 1; y_right < BOARDY && board[x][y] == board[x][y_right]; y_right++)
(gdb)

I see x counting down with the changing board, but y is always 0, so the loop always does the same thing.