c++ - Navigating an Array with Column Boundaries -

let's there square 2 dimensional array of n x n, represented 1 dimension array. let array 5x5, below, , values in array not significant.

std::vector< int > array {     0, 1, 2, 3, 4,     5, 6, 7, 8, 9,     0, 1, 2, 3, 4,     5, 6, 7, 8, 9,     0, 1, 2, 3, 4 }; 

if there 5 rows , 5 columns in array, how can 1 detect if on edge of row? instance, if on index of 9 on 4th row, how can know can go left without changing rows, going right advance next row? how can 1 access cell's neighbors respect edges? index of 9 on 4th row not have right neighbor.

the way can think of how current index, in case is

int index = row * num_cols + col 

and perhaps use modulus (index % 5 == 0) determine if on edge. not determine if can go left or right.

your formula

int index = row * num_cols + col; 

going or down equivalent adding / subtracting num_cols.

is correct. reverse of is

int row = index / num_cols; int col = index % num_cols; 

you know you're on left edge when (index % num_cols) == 0.

you know you're on right edge when (index % num_cols) == num_cols-1.