📜 Lecture 6: 2D Arrays

This lecture expands on arrays, introducing 2D (two-dimensional) arrays, also known as matrices.

Key Concepts

• 2D Array: An "array of arrays". Think of it as a grid or a table with rows and columns.

• Syntax: int a[ROWS][COLUMNS];.

  • int a[3][4]; declares a 2D array with 3 rows and 4 columns.

• Initialization:

  • Method 1 (Flat): int a[3][4] = {1, 2, 3, 4, 5, 6, 8, 9, ...};.
  • Method 2 (Nested): This is clearer. Each inner {} is a row.

    int a[3][3] = { {0, 1, 2},  // Row 0
                    {3, 4, 5},  // Row 1
                    {6, 7, 8} }; // Row 2

• Accessing Elements:

  • You need two indices: a[rowIndex][columnIndex].
  • Both indices start at 0.
  • a[0][0] is the top-left element (e.g., 0 in the example).
  • a[1][1] is the element in the 2nd row, 2nd column (e.g., 4).
  • a[2][2] is the element in the 3rd row, 3rd column (e.g., 8).

• Using Nested Loops: To access every element in a 2D array, you must use nested loops (a loop inside another loop).

  • The outer loop (e.g., i) iterates through the rows.
  • The inner loop (e.g., j) iterates through the columns for each row.

• Example (Reading from User):

  for(int i=0; i<3; i++) {       // Outer loop (rows)
    for(int j=0; j<3; j++) {   // Inner loop (columns)
      cin >> a[i][j];
    }
  }

• Example (Printing):

  for(int i=0; i<3; i++) {
    for(int j=0; j<3; j++) {
      cout << a[i][j];
    }
    cout << endl; // New line after each row
  }