2D vector in C++ with user defined size

A 2D vector is a vector of vector. Like 2D arrays, we can declare and assign values to 2D matrix. 二维vector是由vector组成的vector，和二维数组一样，可以声明和定义二维数组。

// C++ code to demonstrate 2D vector 
#include <iostream> 
#include <vector> // for 2D vector 
using namespace std; 

int main() 
{ 
	// Initializing 2D vector "vect" with 
	// values 
	vector<vector<int> > vect{ { 1, 2, 3 }, 
							{ 4, 5, 6 }, 
							{ 7, 8, 9 } }; 

	// Displaying the 2D vector 
	for (int i = 0; i < vect.size(); i++) { 
		for (int j = 0; j < vect[i].size(); j++) 
			cout << vect[i][j] << " "; 
		cout << endl; 
	} 

	return 0; 
}

Outout :

1 2 3 
4 5 6 
7 8 9

Like Java’s jagged arrays, each row of 2D vector can contain different number of columns. 二维vector的行可以包含不同数量的列。

// C++ code to demonstrate 2D vector where 
// each row is of different size. 
#include <iostream> 
#include <vector> // for 2D vector 
using namespace std; 

int main() 
{ 
	// Initializing 2D vector "vect" with 
	// different number of values in each 
	// row. 
	vector<vector<int> > vect{ { 1, 2 }, 
							{ 4, 5, 6 }, 
							{ 7, 8, 9, 10 } }; 

	// Displaying the 2D vector 
	for (int i = 0; i < vect.size(); i++) { 
		for (int j = 0; j < vect[i].size(); j++) 
			cout << vect[i][j] << " "; 
		cout << endl; 
	} 

	return 0; 
}

Output :

1 2 
4 5 6 
7 8 9 10

Exercise Problem : Define the 2D vector with different sizes of column input by user.
Examples:

Input : Number of rows : 5 
        Number of columns in rows : 
        2 3 4 5 1
Output : 1 2
         1 2 3
         1 2 3 4
         1 2 3 4 5 
         1

Input : Number of rows : 3
        Number of columns in rows : 
        3 2 1
Input : 3 3 2 1
Output : 1 2 3
         1 2
         1

First we take the input of row and and take the input of column of every row.
Now the initialize the memory of every row by the size of column.

// CPP program to create a 2D vector where 
// every row has 
#include <bits/stdc++.h> 
using namespace std; 

int main() 
{ 
	// size of row 
	int row = 5; 
	int colom[] = { 5, 3, 4, 2, 1 }; 

	// Create a vector of vector with size 
	// equal to row. 
	vector<vector<int> > vec(row); 

	for (int i = 0; i < row; i++) { 

		// size of column 
		int col; 
		col = colom[i]; 

		// declare the i-th row to size of column 
		vec[i] = vector<int>(col); 
		for (int j = 0; j < col; j++) 
			vec[i][j] = j + 1; 
	} 

	for (int i = 0; i < row; i++) { 
		for (int j = 0; j < vec[i].size(); j++) 
			cout << vec[i][j] << " "; 
		cout << endl; 
	} 
}

Output:

// C++ code to demonstrate 2D vector 
#include<iostream> 
#include<vector> // for 2D vector 
using namespace std; 

int main() 
{ 
	// Initializing 2D vector "vect" with 
	// values 
	int row;
	cin>>row;
	vector< vector<int> >vec(row);
	for(int i=0; i<row; i++){
		int col;
		cin>>col;
		vec[i] = vector<int>(col);
		for(int j=0; j<col; j++)
		    vec[i][j] = j+1;
	}
	for(int i=0; i<row; i++){
		for(int j=0; j<vec[i].size(); j++)
	        cout<<vec[i][j] << " ";
	    cout<<endl;
	}
	    
	return 0; 
}

output:

5
4 3 2 1 6
1 2 3 4
1 2 3
1 2
1
1 2 3 4 5 6

This article is contributed by Amit Verma. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to [email protected]. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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2D vector in C++ with user defined size

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