Answers for "how to initialize empty vector c++"

initialize vector of vector c++

#include <iostream>
#include <vector>
 
#define M 3
#define N 4
 
int main()
{
  // specify default value to fill the vector elements
  int default_value = 1;
  // first initialize a vector of ints with given default value
  std::vector<int> v(N, default_value);
  // Use above vector to initialize the two-dimensional vector
  std::vector<std::vector<int>> matrix(M, v);
  
  return 0;
}

vector c++ empty it

// clearing vectors
#include <iostream>
#include <vector>

int main ()
{
  std::vector<int> myvector;
  myvector.push_back (100);
  myvector.push_back (200);
  myvector.push_back (300);

  std::cout << "myvector contains:";
  for (unsigned i=0; i<myvector.size(); i++)
    std::cout << ' ' << myvector[i];
  std::cout << 'n';

  myvector.clear(); // making myverctor.empty() == 1
  myvector.push_back (1101);
  myvector.push_back (2202);

  std::cout << "myvector contains:";
  for (unsigned i=0; i<myvector.size(); i++)
    std::cout << ' ' << myvector[i];
  std::cout << 'n';

  return 0;
}

Empty the vector

//C++ STL program to demonstrate example of
//vector::empty() function

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> v1;

    //printing the size of the vector
    cout << "Total number of elements: " << v1.size() << endl;
    //checking whether vector is empty or not
    if (v1.empty())
        cout << "vector is empty." << endl;
    else
        cout << "vector is not empty." << endl;

    //pushing elements
    v1.push_back(10);
    v1.push_back(20);
    v1.push_back(30);
    v1.push_back(40);
    v1.push_back(50);

    //printing the size of the vector
    cout << "Total number of elements: " << v1.size() << endl;
    //checking whether vector is empty or not
    if (v1.empty())
        cout << "vector is empty." << endl;
    else
        cout << "vector is not empty." << endl;

    return 0;
}

c++ how to return an empty vector

return vector<int>();
//or
return{};