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2D vector in C++ STL with user defined size

C++ STL 2D Vector: Here, we are going to learn about the vector of vector or 2D vector in C++ STL, its declaration with user defined size.
Submitted by IncludeHelp, on June 16, 2019

2D Vector in C++ STL

In C++ STL, a 2D vector is a vector of vector.

Declaration

Syntax to declare a 2D vector:

vector<vector<T>> vector_name{ {elements}, {elements}, ...};

Example 1

C++ STL code to declare and print a 2D Vector (with same number of elements).

// C++ STL code to declare and print a 2D Vector
#include <iostream>
#include <vector> // for vectors
using namespace std;

int main()
{
    // Initializing 2D vector "v1" with
    // same number of vector elements
    vector<vector<int> > v1{ { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };

    // Printing the 2D vector's elements
    for (int i = 0; i < v1.size(); i++) {
        for (int j = 0; j < v1[i].size(); j++)
            cout << v1[i][j] << " ";
        cout << endl;
    }

    return 0;
}

Output

1 2 3
4 5 6
7 8 9

Example 2

C++ STL code to declare and print a 2D Vector (with different number of elements).

// C++ STL code to declare and print a 2D Vector
#include <iostream>
#include <vector> // for vectors
using namespace std;

int main()
{
    // Initializing 2D vector "v1" with
    // different number of vector elements
    vector<vector<int> > v1{ { 1, 2, 3 }, { 4, 5 }, { 6, 7, 8, 9 } };

    // Printing the 2D vector's elements
    for (int i = 0; i < v1.size(); i++) {
        for (int j = 0; j < v1[i].size(); j++)
            cout << v1[i][j] << " ";
        cout << endl;
    }

    return 0;
}

Output

1 2 3
4 5
6 7 8 9

Example 3

C++ STL code to declare and print a 2D Vector (Numbers of rows, columns and elements input by the user).

// C++ STL code to declare and print a 2D Vector
#include <iostream>
#include <vector> // for vectors
using namespace std;

int main()
{
    int row;
    int col;

    // Input rows & columns
    cout << "Enter number of rows: ";
    cin >> row;
    cout << "Enter number of columns: ";
    cin >> col;

    // Declaring 2D vector "v1" with
    // given number of rows and columns
    // and initialized with 0
    vector<vector<int> > v1(row, vector<int>(col, 0));

    // Input vector's elements
    for (int i = 0; i < v1.size(); i++) {
        for (int j = 0; j < v1[i].size(); j++) {
            cout << "Enter element: ";
            cin >> v1[i][j];
        }
    }

    // Printing the 2D vector's elements
    cout << "2D vector elements..." << endl;
    for (int i = 0; i < v1.size(); i++) {
        for (int j = 0; j < v1[i].size(); j++)
            cout << v1[i][j] << " ";
        cout << endl;
    }
    return 0;
}

Output

Enter number of rows: 3
Enter number of columns: 4
Enter element: 1
Enter element: 2
Enter element: 3
Enter element: 4
Enter element: 5
Enter element: 6
Enter element: 7
Enter element: 8
Enter element: 9
Enter element: 10
Enter element: 11
Enter element: 12
2D vector elements...
1 2 3 4
5 6 7 8
9 10 11 12