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How to join two Arrays using STL in C++?
• Difficulty Level : Basic
• Last Updated : 19 Mar, 2019

Given two arrays, join these two arrays using STL in C++.

Example:

Input:
arr1[] = {1, 45, 54, 71, 76, 12},
arr2[] = {1, 7, 5, 4, 6, 12}
Output: {1, 4, 5, 6, 7, 12, 45, 54, 71, 76}

Input:
arr1[] = {1, 7, 5, 4, 6, 12},
arr2[] = {10, 12, 11}
Output: {1, 4, 5, 6, 7, 10, 11, 12}

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: Joining can be done with the help of set_union() function provided in STL.

Syntax:

```set_union (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result);
```

Below is the implementation of the above approach:

 `// C++ program to join two Arrays``// using set_union() in STL`` ` `#include ``using` `namespace` `std;`` ` `int` `main()``{`` ` `    ``// Get the array``    ``int` `arr1[] = { 1, 45, 54, 71, 76, 12 };``    ``int` `arr2[] = { 1, 7, 5, 4, 6, 12 };`` ` `    ``// Compute the sizes``    ``int` `n1 = ``sizeof``(arr1) / ``sizeof``(arr1[0]);``    ``int` `n2 = ``sizeof``(arr2) / ``sizeof``(arr2[0]);`` ` `    ``// Sort the arrays``    ``sort(arr1, arr1 + n1);``    ``sort(arr2, arr2 + n2);`` ` `    ``// Print the array``    ``cout << ``"First Array: "``;``    ``for` `(``int` `i = 0; i < n1; i++)``        ``cout << arr1[i] << ``" "``;``    ``cout << endl;`` ` `    ``cout << ``"Second Array: "``;``    ``for` `(``int` `i = 0; i < n2; i++)``        ``cout << arr2[i] << ``" "``;``    ``cout << endl;`` ` `    ``// Initialise a vector``    ``// to store the merged values``    ``// and an iterator``    ``// to traverse this vector``    ``vector<``int``> v(n1 + n2);``    ``vector<``int``>::iterator it, st;`` ` `    ``it = set_union(arr1, arr1 + n1,``                   ``arr2, arr2 + n2,``                   ``v.begin());`` ` `    ``// Print the merged array``    ``cout << ``"\nAfter joining:\n"``;``    ``for` `(st = v.begin(); st != it; ++st)``        ``cout << *st << ``", "``;``    ``cout << ``'\n'``;`` ` `    ``return` `0;``}`
Output:
```First Array: 1 12 45 54 71 76
Second Array: 1 4 5 6 7 12

After joining:
1, 4, 5, 6, 7, 12, 45, 54, 71, 76,
```
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