size in vector c++ code example

Example 1: cpp vector structure

#include <vector>

typedef struct test1 {
  int a;
  char b;
} TOTO;

std::vector<TOTO> _v;

_v.push_back((TOTO){10, 'a'});
_v[0].a = 101;

Example 2: declare vector of size n in c++

#include <vector>

auto n = 20
// create a vector with n=20 integer elements
std::vector<int> arr(n);