2D Arrays and Matrices

Grids and Tables

int matrix[3][3] = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

cout << matrix[1][2];  // 6  (row 1, column 2)

for (int r = 0; r < 3; r++) {
    for (int c = 0; c < 3; c++)
        cout << matrix[r][c] << " ";
    cout << endl;
}

Dynamic 2D with vector

vector<vector<int>> grid = {
    {1, 2, 3},
    {4, 5, 6}
};
grid[0].size()   // 3 columns
grid.size()      // 2 rows

Your Task

Write matrixTrace(vector<vector<int>> m) that returns the trace — sum of the main diagonal elements (where row index == column index).