Find sums of half diagonals
int diag1_left = 0 , diag1_right = 0 ; int diag2_left = 0 , diag2_right = 0 ; for ( int i = 0 , j = n - 1 ; i < n ; i ++ , j -- ) { if ( i < n / 2 ) { diag1_left += mat [ i ] [ i ] ; diag2_left += mat [ j ] [ i ] ; } else if ( i > n / 2 ) { diag1_right += mat [ i ] [ i ] ; diag2_right += mat [ j ] [ i ] ; } } return ( diag1_left == diag2_right && diag2_right == diag2_left && diag1_right == diag2_left && diag2_right == mat [ n / 2 ] [ n / 2 ] ) ; }