check if index is out of bounds to satisfy if conditions - c++

Question

Hello I am practicing working with 2d arrays in c++ and my question is for example if I want to check if 4 has either 0 or 11 to the north , east, south, west as neighbour it should return false.
this is my if
if((grid[0-1][0] == 0 || grid[0-1][0] == 11 ) &&
(grid[0+1][0] == 0 || grid[0+1][0] == 11 ) &&
(grid[0][0+1] == 0 || grid[0][0+1] ==11) &&
(grid[0][0-1] == 0 || grid[0][0-1] ==11 ))
{
return false;
}
Now my problem is since west of 4 and north of four is out of bounds it will never return false.
How could I optimise my if condition to make it return false?
This is my 2d array
int grid[ROW][COL] = {{ 4, 11, 1, 1 },
{ 0, 0, 1, 0 },
{ 0, 1, 5, 0},
{ 0, 5, 0,0 } };

Answer 1

TL;DR
you are missing boundary conditions
// Boundary Conditions
if( i == ROW || j == COL || i < 0 || j < 0 )
return false;
Based on the question the matrix is defined as
#define ROW 4
#define COL 4
int grid[ROW][COL] = {{ 4, 11, 1, 1 },
{ 0, 0, 1, 0 },
{ 0, 1, 5, 0},
{ 0, 5, 0,0 } };
given a cell at row i and col j denoted by cordinated i, j the visualization in a 2-D array for that will look like this
i-1, j-1 i-1, j i-1,j+1
i, j-1 i, j i,j+1
i+1, j-1 i+1, j i+1,j+1
from above we can now deduce the corresponding cordinates/points reference to given i,j
i,j ---> North( i-1, j )
i,j ---> South( i+1, j )
i,j ---> East( i , j+1)
i,j ---> West( i , j-1)
now we can write a small function to check if a given value at any cell denoted by i and j is true or not, this below function does similar .. checks if supplied coordinates are within boundary and if the value at grid[j]j] matches what we need to match
bool Check( int grid[ROW][COL], int expected, int i, int j )
{
// Boundary Conditions
if( i == ROW || j == COL || i < 0 || j < 0 )
return false;
return ( grid[i][j] == expected );
}
Now time to put the North, South, West, East calculation to code and expose them as nice functions,
bool northHas( int grid[ROW][COL], int expected, int i, int j )
{
return check(grid, expected, i-1, j );
}
bool southHas( int grid[ROW][COL], int expected, int i, int j )
{
return check(grid, expected, i+1, j );
}
bool eastHas( int grid[ROW][COL], int expected, int i, int j )
{
return check(grid, expected, i, j+1 );
}
bool westHas( int grid[ROW][COL], int expected, int i, int j )
{
return check(grid, expected, i, j-1 );
}
each of these functions above exposes a nicer interface to deal with what logic program wants to do
if( (northHas( grid, 0, i, j ) || northHas( grid, 11, i, j)) &&
( eastHas( grid, 0, i, j ) || eastHas( grid, 11, i, j)) &&
(southHas( grid, 0, i, j ) || southHas( grid, 11, i, j)) &&
( westHas( grid, 0, i, j ) || westHas( grid, 11, i, j)) )
{
return false
}