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    <p><code>x</code> = x position<br> <code>y</code> = y position<br> <code>cols</code> = number of columns across in your grid</p> <p><code>(y * cols) + x</code> = index in array absolute value for any x, y</p> <p>you could generalize this in a function:</p> <pre><code>int get_index(int x, int y, int gridcols) { return (gridcols * y) + x; } </code></pre> <p>It should be noted that this works for ZERO BASED INDICES. This is assuming I am understanding what you're talking about at all...</p> <p>As for the second question, for any colored element you have, you should keep a value in memory (possibly stored in a structure) that keeps track of its position so you don't have to search for it at all.</p> <pre><code>struct _THING { int xpos; int ypos; }; </code></pre> <p>Using the get_index() function, you could find the index of the grid cell below it by calling like this:</p> <pre><code>index_below = get_index(thing.x, thing.y + 1, gridcols); thing.y++; // increment the thing's y now since it has moved down </code></pre> <p>simple...</p> <p>IF YOU WANT TO DO IT IN REVERSE, as in finding the x,y position by the array index, you can use the modulus operator and division.</p> <pre><code>ypos = array_index / total_cols; // division without remainder xpos = array_index % total_cols; // gives the remainder </code></pre> <p>You could generalize this in a function like this:</p> <pre><code>// x and y parameters are references, and return values using these references void get_positions_from_index(int array_index, int total_columns, int&amp; x, int&amp; y) { y = array_index / total_columns; x = array_index % total_columns; } </code></pre> <p>Whenever you're referring to an array index, it must be zero-based. However, when you are referring to the number of columns, that value will be 1-based for the calculations. x and y positions will also be zero based.</p>
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