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How do I change a repeating if statement to something more efficient.

test1234 (24)
I have a minesweeper game and If there is already a mine in the location, I need to find another spot. I am using tons of if else statements. If I want to make it work 100% I would have to use an infinite amount of them. There has to be another type of loop that would to this.
I have a loop to perform the function for how ever many mines the user wants.

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  void assignMines(values array[row][column])
{
    int i = rand()%5;
    int j = rand()%5;
    if (array[i][j] == MINE)
    {
        int k = rand()%5;
        int l = rand()%5;
        if (array[k][l] == MINE)
        {
            int m = rand()%5;
            int n = rand()%5;
            if(array[m][n] == MINE)
            {
                int o = rand()%5;
                int p = rand()%5;
                if(array[o][p] == MINE)
                {
                    int q = rand()%5;
                    int r = rand()%5;
                    if(array[q][r] == MINE)
                    {
                        int s = rand()%5;
                        int t = rand()%5;
                        array[s][t] = MINE;
                    }else
                    {
                        array[q][r] = MINE;
                    }
                }else
                {
                    array[o][p] = MINE;
                }
            }else
            {
                array[m][n] = MINE;
            }
        }else
        {
            array[k][l] = MINE;
        }
    }else
    {
        array[i][j] = MINE;
    }
int main()
int minecount;
cout << "Enter number of mines to place on board (5 - 10):";
cin >> minecount;
for (int i=0;i<minecount;i++)
{
    assignMines(array);
}
Last edited on
test1234 (24)
It most of the time works for 5 mines but the bigger amount of mines you want the more chance of it randomly picking same spot.
mbozzi (3932)
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for (int mines_placed = 0; mines_placed < total_mines;) { 
  int row = rand() % 5, col = rand() % 5;
  if (array[row][col] == MINE) continue; // there is already a mine here
  array[row][col] = MINE; // else place the mine
  ++mines_placed;
}


While in the limiting case the loop never halts, in practice that that isn't a problem -- your computer is fast, and the loop will iterate many millions of times before any delay is noticeable.

In limited cases it is potentially useful to create a grab bag -- to simulate "draw without replacement". A grab bag works by storing a set of candidates and shuffling them, then iterating over the shuffled candidates. That guarantees a linear bound on the amount of time spent, even as the ratio of occupied to open spaces approaches 1.

As a general note, if you need a structure which is nested very deeply (or even which should be nested to a variable depth) you can model that with functions which call themselves. The concept is called "recursion". It doesn't apply here, but your approach hints at a recursive solution.
Last edited on
JLBorges (13770)
> simulate "draw without replacement"

Here, it would be something like this:

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template < std::size_t NROWS, std::size_t NCOLS >
void assign_mines( value (&array)[NROWS][NCOLS], std::size_t num_mines )
{
    // fill the first 'num_mines' positions with mines
    std::fill_n( std::begin( array[0] ), std::min( NROWS*NCOLS, num_mines ), MINE ) ;

    // shuffle the elements around so that the mines are randomly distributed
    static std::mt19937 rng( std::random_device{}() ) ;
    std::shuffle( std::begin( array[0] ), std::end( array[NROWS-1] ), rng ) ;
}

http://coliru.stacked-crooked.com/a/55f186431cac4895
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