# C++ Valarray Library - atan Function

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## Description

It returns a valarray object containing the principal values of the arc tangent of all the elements of x, expressed in radians, in the same order.

## Declaration

Following is the declaration for std::atan function.

```template<class T> valarray<T> atan (const valarray<T>& x);
```

### C++11

```template<class T> valarray<T> atan (const valarray<T>& x);
```

## Parameters

x − It is containing elements of a type for which the unary function abs is defined.

## Return Value

It returns a valarray object containing the principal values of the arc tangent of all the elements of x, expressed in radians, in the same order.

## Exceptions

Basic guarantee − if any operation performed on the elements throws an exception.

## Data races

All elements effectively copied are accessed.

## Example

In below example explains about std::atan function.

```#include <iostream>
#include <cstddef>
#include <cmath>
#include <valarray>

int main () {
double val[] = {0.0, 0.25, 0.5, 0.75, 1.0};
std::valarray<double> foo (val,5);

std::valarray<double> bar = atan (foo);

std::cout << "foo:";
for (std::size_t i=0; i<foo.size(); ++i)
std::cout << ' ' << foo[i];
std::cout << '\n';

std::cout << "bar:";
for (std::size_t i=0; i<bar.size(); ++i)
std::cout << ' ' << bar[i];
std::cout << '\n';

return 0;
}
```

Let us compile and run the above program, this will produce the following result −

```foo: 0 0.25 0.5 0.75 1
bar: 0 0.244979 0.463648 0.643501 0.785398
```
valarray.htm