# Elements present in first array and not in second using STL in C++

Given two arrays, the task is that we find numbers which are present in first array, but not present in the second array, using STL in C++

**Examples:**

Input:a[] = {1, 2, 3, 4, 5, 10}, b[] = {2, 3, 1, 0, 5}Output:4 10Input:a[] = {4, 3, 5, 9, 11}, b[] = {4, 9, 3, 11, 10};Output:5

**Approach:** In STL, the set_difference() method can be used to find the ‘A-B’ where A is the first array and B is the second array.

**Syntax:**

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

Below is the implementation of the above approach:

`// C++ simple program to` `// find elements which are` `// not present in second array` ` ` `#include <bits/stdc++.h>` `using` `namespace` `std;` ` ` `// Function for finding` `// elements which are there` `// in a[] but not in b[].` `void` `findMissing(` `int` `a[], ` `int` `b[],` ` ` `int` `n, ` `int` `m)` `{` ` ` ` ` `// Declare a vector to store the result` ` ` `vector<` `int` `> v(n + m);` ` ` ` ` `// And an iterator to traverse the vector` ` ` `vector<` `int` `>::iterator it;` ` ` ` ` `// Sort the given arrays` ` ` `sort(a, a + n);` ` ` `sort(b, b + m);` ` ` ` ` `// Find the elements in a[]` ` ` `// which are not in b[]` ` ` `it = set_difference(a, a + n, b, b + m, v.begin());` ` ` ` ` `// Now resize the vector to the existing count` ` ` `v.resize(it - v.begin());` ` ` ` ` `// Print the results` ` ` `cout << ` `"The elements in a[]"` ` ` `<< ` `" which are not in b[]:\n"` `;` ` ` `for` `(it = v.begin(); it != v.end(); ++it)` ` ` `cout << *it << ` `" "` `;` ` ` `cout << endl;` `}` ` ` `// Driver code` `int` `main()` `{` ` ` `int` `a[] = { 1, 2, 6, 3, 4, 5 };` ` ` `int` `b[] = { 2, 4, 3, 1, 0 };` ` ` `int` `n = ` `sizeof` `(a) / ` `sizeof` `(a[0]);` ` ` `int` `m = ` `sizeof` `(b) / ` `sizeof` `(b[1]);` ` ` `findMissing(a, b, n, m);` ` ` `return` `0;` `}` |

**Output:**

The elements in a[] which are not in b[]: 5 6

Want to learn from the best curated videos and practice problems, check out the

**C++ Foundation Course**for Basic to Advanced C++ and**C++ STL Course**for foundation plus STL. To complete your preparation from learning a language to DS Algo and many more, please refer**Complete Interview Preparation Course****.**