# Array sum in C++ STL

• Difficulty Level : Basic
• Last Updated : 28 Oct, 2017

In C++, we can quickly find array sum using accumulate()

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 `// C++ program to demonstrate working of accumulate()``#include  ``#include      ``using` `namespace` `std;``  ` `// User defined function that returns sum of``// arr[] using accumulate() library function.``int` `arraySum(``int` `a[], ``int` `n) ``{``    ``int` `initial_sum  = 0; ``    ``return` `accumulate(a, a+n, initial_sum);``}``  ` `int` `main() ``{``    ``int` `a[] = {5 , 10 , 15} ;``    ``int` `n = ``sizeof``(a)/``sizeof``(a[0]);``    ``cout << arraySum(a, n);``    ``return` `0;``}`

Output:

```30
```

Sum of vector

 `// C++ program to demonstrate working of accumulate()``#include  ``#include  ``#include      ``using` `namespace` `std;``  ` `// User defined function that returns sum of``// arr[] using accumulate() library function.``int` `arraySum(vector<``int``> &v) ``{``    ``int` `initial_sum  = 0; ``    ``return` `accumulate(v.begin(), v.end(), initial_sum);``}``  ` `int` `main() ``{``    ``vector<``int``> v{5 , 10 , 15} ;``    ``cout << arraySum(v);``    ``return` `0;``}`

Output:

```30
```

We can also use a custom function in accumulate. Refer numeric header in C++ STL | Set 1 (accumulate() and partial_sum()) for details.

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