# valarray atan() function in C++

• Last Updated : 24 Oct, 2018

The atan() function is defined in valarray header file. This function is used to calculate arc tangent of the value of each element in valarray and returns a valarray containing the arc tangent of all the elements.

Syntax:

```atan(varr);
```

Parameter: This function takes a mandatory parameter varr which represents valarray.

Returns: This function returns a valarray containing the arc tangent of all the elements.

Below programs illustrate the above function:

Example 1:-

 `// C++ program to demonstrate``// example of atan() function.`` ` `#include ``using` `namespace` `std;`` ` `int` `main()``{``    ``// Initializing valarray``    ``valarray<``double``>``        ``varr = { 0, 0.25, 0.5, 0.75, 1 };`` ` `    ``// Declaring new valarray``    ``valarray<``double``> varr1;`` ` `    ``// use of atan() function``    ``varr1 = ``atan``(varr);`` ` `    ``// Displaying new elements value``    ``cout << ``"The new valarray with"``         ``<< ``" manipulated values is : "``         ``<< endl;`` ` `    ``for` `(``double``& x : varr1) {``        ``cout << x << ``" "``;``    ``}`` ` `    ``cout << endl;`` ` `    ``return` `0;``}`

Output:

```The new valarray with manipulated values is :
0 0.244979 0.463648 0.643501 0.785398
```

Example 2:-

 `// C++ program to demonstrate``// example of atan() function.`` ` `#include ``using` `namespace` `std;``int` `main()``{``    ``// Initializing valarray``    ``valarray<``double``>``        ``varr = { 0.2, 0.14, 5.0, 0.0 };`` ` `    ``// Declaring new valarray``    ``valarray<``double``> varr1;`` ` `    ``// use of atan() function``    ``varr1 = ``atan``(varr);`` ` `    ``// Displaying new elements value``    ``cout << ``"The new valarray with"``         ``<< ``" manipulated values is : "``         ``<< endl;`` ` `    ``for` `(``double``& x : varr1) {``        ``cout << x << ``" "``;``    ``}`` ` `    ``cout << endl;`` ` `    ``return` `0;``}`

Output:

```The new valarray with manipulated values is :
0.197396 0.139096 1.3734 0
```

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