Check out example codes for "declare vectors c++". It will help you in understanding the concepts better.

Code Example 1

``````// CPP program to initialize a vector from
// another vector.
#include <bits/stdc++.h>
using namespace std;

int main()
{
vector<int> vect1{ 10, 20, 30 };

vector<int> vect2(vect1.begin(), vect1.end());

for (int x : vect2)
cout << x << " ";

return 0;
}``````

Code Example 2

``std::vector<type> name;``

Code Example 3

``````// CPP program to create an empty vector
// and push values one by one.
#include <bits/stdc++.h>
using namespace std;

int main()
{
// Create an empty vector
vector<int> vect;

vect.push_back(10);
vect.push_back(20);
vect.push_back(30);

for (int x : vect)
cout << x << " ";

return 0;
}``````

Code Example 4

``````// First include the vector library:
#include <vector>

// The syntax to create a vector looks like this:
std::vector<type> name;

// We can create & initialize "lol" vector with specific values:
std::vector<double> lol = {66.666, -420.69};

// it would look like this: 66.666 | -420.69``````

Code Example 5

``````vector<int> vec;
//Creates an empty (size 0) vector

vector<int> vec(4);
//Creates a vector with 4 elements.

/*Each element is initialised to zero.
If this were a vector of strings, each
string would be empty. */

vector<int> vec(4, 42);

/*Creates a vector with 4 elements.
Each element is initialised to 42. */

vector<int> vec(4, 42);
vector<int> vec2(vec);

/*The second line creates a new vector, copying each element from the
vec into vec2. */``````

Code Example 6

``````// CPP program to initialize a vector like
// an array.
#include <bits/stdc++.h>
using namespace std;

int main()
{
vector<int> vect{ 10, 20, 30 };

for (int x : vect)
cout << x << " ";

return 0;
}``````

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