Creating 2-D Boolean Vector with False value

Question

i want too create a 2-D vector of Boolean type with Size n x n . but i don't want to use two for loop to assign false to every index instead of assign directly while creating this vector. syntax is:- vector<vector<bool>> V(n,false)

but it gives me error

463035818_is_not_an_ai · Answer 1 · 2020-12-29T16:12:24.750

2

There is a constructor that takes a count and an element, but false is not a std::vector<bool>. You want

std::vector<std::vector<bool>> V(n, std::vector<bool>(n,false)  );
                               //   |---- inner vectors  ----|

Two disclaimer:

Use std::vector<bool> with caution. It is not like other std::vectors (see eg Alternative to vector<bool>).

A vector of vectors is rarely the best data structure. The power of a std::vector is its data locality, however a std::vector<std::vector<T>> does not have this feature (only elements of the inner vectors are contiguous).

edited Dec 29 '20 at 16:12

answered Dec 29 '20 at 13:12

463035818_is_not_an_ai

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Indeed; `std::vector` of size _n×n_ would be far superior. – Asteroids With Wings Dec 29 '20 at 13:25

score 1 · Answer 2 · answered Dec 29 '20 at 13:12

vector<vector> V(n,false) this gives an error because you are not declaring size of each v[i] thus, it can not assign each of v[i][j] to false.

you can use vector<vector> v(n, vector (n, false));

Code:

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    cin>>n;
    vector<vector<bool>> v(n, vector<bool> (n, false));

    for(int i=0;i<n;i++)
    {
        for(int j=0;j<v[i].size();j++)
        {
            cout<<v[i][j]<<" ";
        }
        cout<<'\n';
    }
}

Ans:

Creating 2-D Boolean Vector with False value

2 Answers2