Array of Vectors in C++ STL

Prerequisites: C++ STL Arrays and C++ STL Vector.

A group of items kept in consecutive memory region is known as an array. It is to group similar objects of the same type in storage. As a result, it is simpler to access the pieces contained there thanks to their positions.

Vectors are referred to as dynamic arrays because they may dynamically resize themselves when an element is added or removed, with the container taking care of its storage automatically.By including the vector header file as #includevector> at the beginning of the program , these vectors are used in C++ program s.

As a result, an array of vectors is a two-dimensional array with a set number of rows and a variable number of rows per vector. Iterators can be used to traverse and access the vectors that are stored in each index of an array.

Syntax:

vector <data_type>identifier[size];

We can break down the syntax for a vector array into its component pieces because we have already seen that it is vector <data_type>identifier[size].

Example:

Vector <int>A [5];
Where A is the vectors array of int of size 5

Insertion:

The push back() function is used for vector array insertion.

Example:

for I n [0,n) {
          A[i]. push_back (35)
      }

The above pseudo-code inserts element 35 into the vector int> A[n] at every index.

Example:

#include <iostream>
#include <vector>
usingnamespacestd;
int main()
{
    // quantity of vectors
intn;
    court<<"Enter number of vectors in array : ";
cin>>n;
    // creating array of vectors "vec" with size n(vectors)
    vector<int>vec [n];
    // input components are added to each vector
for (inti=0; i<n; i++){
cout<<"Enter number of elements in vector "<<i+1<<" : ";
intnum;
cin>>num;
cout<<"Enter elements into vector "<<i+1<<" : ";
for (int j=0; j<num; j++){
inttemp;      // to pull a component from the input back into a vector
cin>>temp;
vec[i].push_back(temp);
        }
    }
    // printing vector-based elements
cout<<"Method 1 : Using size() method"<<endl;
cout<<"Elements are : "<<endl;
for(inti=0; i<n; i++){
cout<<"Vector "<<i+1<<" : ";
int size = vec[i].size();
for(int j=0; j<size; j++)
cout<<vec[i][j]<<" ";
cout<<endl;
    }
cout<<"Method 2 : Using iterators method"<<endl;
for(inti=0; i<n; i++){
cout<<"Vector "<<i+1<<" : ";
for(auto it = vec[i].begin();it != vec[i].end(); it++)
cout<< *it << ' ';
cout<<endl;
    }
return0;
}

Output:

Working

It is quite simple to carry out certain fundamental operations on an array using the STL library, including as sorting, searching, adding up the elements, and determining the array's minimum and maximum elements.

Traversal

Iterators are used to execute vector array traversal.

Example:

For I in [0,n) {
         For (iterator it = A [i]. begin ();
            It! =A[i].end (); it++) {
          Print (*it)
        }
     }

By using the beginning iterator, A[i]. begin() and the ending iterator A[i]. end, the pseudo-code explores the vector int> A[n] at each index (). Since iterators are pointers pointing to elements in vector int> A[n], it uses (*it) to access the element.

The program used to demonstrate the insertion into the vector array is shown below.

Example:

// a C++ application to display
// a vector array
  
#include <iostream>
#include <vector>
usingnamespacestd;
  
// declaring a vector array
// globally
vector<int>v[5];
  
// The ability to introduce elements
// in a vector array
voidinsertionInArrayOfVectors()
{
  
    for (inti = 0; i< 5; i++) {
  
        // Adding components at each
        // using push back in row I ()
        // a vectorized function
        for (int j = i + 1; j < 5; j++) {
            v[i].push_back(j);
        }
    }
}
  
// Function to print elements from a vector array
voidprintElements()
{
  
    // Vectors are traversed to print
    // elements kept there
    for (inti = 0; i< 5; i++) {
  
        cout<< "Elements at index "
             <<i<< ": ";
  
        // each column displaying a different element
        // The initial iterator is begin(),
        // The terminating iterator is end().
        for (auto it = v[i].begin();
             it != v[i].end(); it++) {
  
            // (*it) is used to get the
            // iterator value is
           //indicating
            cout<< *it << ' ';
        }
        cout<<endl;
    }
}
  
// Function that displays an array
// Using vectors
voidarrayOfVectors()
{
    // adding elements to an array
    // using vectors
    insertionInArrayOfVectors();
  
    // Print the array's stored elements.
    // using vectors
    printElements();
}
  
// driver's code
int main()
{
    arrayOfVectors();
    return0;
}
    return0;
}

Output: