Question

I am generating random Nos to store my matrix index for row and column . That is different row and column index Nos every time not repeat. But some time same value is generating.How to rectify this problem.

This is what i written .. for example

4 * 4 Matrix. i am running with loop and storing date

int i;
for (i=0;i<6;i++)
  {

  Row    =     arc4random() % 4 ;
  Column =     arc4random() % 4;

  CGFloat xOffset1 = (block.contentSize.width+350)+((block.contentSize.height-15)*Column);  
  FireBlock.position = ccp(xOffset1,Row*15);

  statement 1--- store Column;
  statement 2--- store Row;
}

Answer 1

With only 16 different combinations, I’d write all of them in an array, shuffle the array, then select from the array.

struct row_col_index {
    int row;
    int column;
};

/* ... */
    struct row_col_index all_combinations[4*4] = {
        {0, 0}, {0, 1}, {0, 2}, {0, 3},
        {1, 0}, {1, 1}, {1, 2}, {1, 3},
        {2, 0}, {2, 1}, {2, 2}, {2, 3},
        {3, 0}, {3, 1}, {3, 2}, {3, 3},
    };

    shuffle(all_combinations);
    for (int i = 0; i < 6; i++) {
        Row = all_combinations[i].row;
        Column = all_combinations[i].column;
        /* ... */
    }
/* ... */