如何在C中将2d数组元素下移

Question

I am trying to shift the contents of a 2d array down when implementing Tetris in C. This is to move the blocks down. The code works but its not moving elements once only, See the image for the problem(The number in the top left corner is the random number that determines the block type). Any help appreciated. Below is the array shifting code:

//Declare size of board
    int board [22][10] = {};

 //Shift down
    for(i=2;i<20;i++)
    {
        for(z=1;z<10;z++)
        {
            board[i+1][z] = board[i][z];
        }
    }

http://i61.tinypic.com/xlb58g.jpg

Answer 1

Whenever you shift the contents of an array, you must work in the opposite direction then the shifting. In your case, you need to invert the direction of your outer loop:

int board [22][10] = {};

for(i = 20; i-- > 2; ) {
    for(z=1; z<9; z++) {
        board[i+1][z] = board[i][z];
    }
}

This allows the row of unused values to rise up in the array like a bubble.

---

Edit:
The code above was written to match the apparent intended behavior of the code posted in the question. If the entire array is to be moved, use this code:

for(i = sizeof(board)/sizeof(*board) - 1; i--; ) {
    for(z = 0; z < sizeof(*board)/sizeof(**board); z++) {
        board[i+1][z] = board[i][z];
    }
}