C++ Two-Dimensional Arrays

[qingquan-li]

Concept: A two-dimensional array is like several identical arrays put together. It is useful for storing multiple sets of data.

double array[Rows][Columns];

// Assigns the value 99.5 to the element at
// row#2 column#1 of the scores array:
scores[1][0] = 99.5;

1. Two-dimensional array initialization

#include <iostream>
using namespace std;

int main() {
    const int ROWS = 3;
    const int COLUMNS = 4;
    // The extra braces that enclose each row's initialization list
    // is optional.
    // int num_ppl[ROWS][COLUMNS] = {
    //     4, 5, 2, 3, 0, 0, 5, 5, 5, 4, 2, 0
    // };
    int num_ppl[ROWS][COLUMNS] = {{4, 5, 2, 3},
                                  {0, 0, 5, 5},
                                  {5, 4, 2, 0}
                                 };
    
    for (int i = 0; i < ROWS; i++) {
        for (int j = 0; j < COLUMNS; j++) {
            cout << num_ppl[i][j] << " ";
        }
        cout << endl;
    }
    return 0;
}

Output:

4 5 2 3 
0 0 5 5 
5 4 2 0 

2. Passing Two-Dimensional Arrays to Functions

When a two-dimensional array is passed to a function, the parameter type must contain a size declarator for the number of columns.

Here is the header for the function print_2D_array below:

void print_2D_array(int arr[][COLUMNS], int rows)

#include <iostream>

using namespace std;

const int COLUMNS = 4;

// Function prototype:
void print_2D_array(int[][COLUMNS], int);

int main() {
    const int ROWS = 3;
    int num_ppl[ROWS][COLUMNS] = {{1, 2, 2, 3},
                                  {0, 0, 5, 5},
                                  {5, 4, 2, 0}
    };

    print_2D_array(num_ppl, ROWS);

    return 0;
}

void print_2D_array(int arr[][COLUMNS], int rows) {
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < COLUMNS; j++) {
            cout << arr[i][j] << " ";
        }
        cout << endl;
    }
}

Output:

1 2 2 3 
0 0 5 5 
5 4 2 0