Initialize a vector in C++ (7 different ways)

01 Jun, 2022
The following are different ways to create and initialize a vector in C++ STL
1. Initializing by pushing values one by one :
CPP
// CPP program to create an empty vector// and push values one by one.#include <iostream>#include <vector>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;}
10 20 30 
2. Specifying size and initializing all values :
CPP
// CPP program to create an empty vector// and push values one by one.#include <iostream>#include <vector>using namespace std; int main(){    int n = 3;     // Create a vector of size n with    // all values as 10.    vector<int> vect(n, 10);     for (int x : vect)        cout << x << " ";     return 0;}
10 10 10 
3. Initializing like arrays :
CPP
// CPP program to initialize a vector like// an array.#include <iostream>#include <vector>using namespace std; int main(){    vector<int> vect{ 10, 20, 30 };     for (int x : vect)        cout << x << " ";     return 0;}
10 20 30 
4. Initializing from an array :
CPP
// CPP program to initialize a vector from// an array.#include <iostream>#include <vector>using namespace std; int main(){    int arr[] = { 10, 20, 30 };    int n = sizeof(arr) / sizeof(arr[0]);     vector<int> vect(arr, arr + n);     for (int x : vect)        cout << x << " ";     return 0;}
10 20 30 
5. Initializing from another vector :
CPP
// CPP program to initialize a vector from// another vector.#include <iostream>#include <vector>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;}
10 20 30 
6. Initializing all elements with a particular value :
CPP
#include <iostream>#include <vector>using namespace std; int main(){    vector<int> vect1(10);    int value = 5;    fill(vect1.begin(), vect1.end(), value);    for (int x : vect1)        cout << x << " ";}
5 5 5 5 5 5 5 5 5 5 
7. Initialize an array with consecutive numbers using std::iota :
C++
// CPP program to initialize an array with consecutive// numbers#include <iostream>#include <numeric>using namespace std; int main(){    int arr[5];    iota(arr, arr + 5, 1);    for (int i = 0; i < 5; i++) {        cout << arr[i] << " ";    }    return 0;}
1 2 3 4 5 
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