Multidimensional arrays
- C++ course
- Beginner
- Lesson 56/116
- 5 min
Learn multidimensional arrays as matrices with int[][].
Multidimensional arrays
To hold data with more than one dimension you use a multidimensional array. The most common example is a 2D matrix: int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}};.
The first dimension is the row count, the second the column count. matrix[i][j] gives the element at row i, column j. For example matrix[1][0] is the first element of the second row. You can picture the matrix as a grid.
Walking a matrix
To walk every element of a matrix you use two nested for loops. The outer loop covers rows, the inner covers columns: for (int i = 0; i < 2; i++) for (int j = 0; j < 3; j++) std::cout << matrix[i][j];.
This is called a nested loop. For each row, all columns are walked, then the outer loop moves to the next row. To print the matrix row by row you can add a std::endl at the end of each row.
Practice Print a matrix element
Declare a 2x3 matrix as int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}}; and print the first element of the second row with std::cout << matrix[1][0];. The output must be 4.
Starter code
#include <iostream>
int main() {
// Declare a 2x3 matrix and print matrix[1][0]
return 0;
}Sample solution
#include <iostream>
int main() {
int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}};
std::cout << matrix[1][0] << std::endl;
return 0;
}Expected output
4
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 How many elements does int m[2][3] hold?
int m[2][3];- 6 Correct answer
- 2
- 3
- 5
Explanation: 2 rows × 3 columns = 6 elements.
2 Write the multidimensional access
int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}};
std::cout << ____;int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}};
std::cout << matrix[1][2];Explanation: matrix[1][2] is the third element of the second row (6).
3 Match each matrix concept to its meaning
| Term | Meaning |
|---|---|
matrix[0] |
First row |
matrix[i][j] |
Row i, column j |
[2][3] |
2 rows 3 columns |
{{1,2,3},{4,5,6}} |
2x3 initial values |