how to change an element in a vector c++ code example

Example 1: convert vector to set c++

#include <set>
std::set<std::string> set_name(vector_name.begin(), vector_name.end());

Example 2: 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;
}