# C++ atan()

The atan() function in C++ returns the inverse tangent of a number (argument) in radians.

This function is defined in <cmath> header file.

`[Mathematics] tan-1x = atan(x) [In C++ Programming];`

## atan() prototype [As of C++ 11 standard]

```double atan(double x);
float atan(float x);
long double atan(long double x);
double atan (T x); // For integral type```

## atan() Parameters

The atan() function takes a single mandatory argument (can be positive, negative, or zero)

## atan() Return value

The atan() function returns the value in the range of [-π/2, π/2].

## Example 1: How atan() works?

``````#include <iostream>
#include <cmath>

using namespace std;

int main()
{
double x = 57.74, result;
result = atan(x);

cout << "atan(x) = " << result << " radians" << endl;

// Output in degrees
cout << "atan(x) = " << result*180/3.1415 << " degrees" << endl;

return 0;
}``````

When you run the program, the output will be:

```atan(x) = 1.55348 radians
atan(x) = 89.0104 degrees```

## Example 2: atan() function with integral type

``````#include <iostream>
#include <cmath>
#define PI 3.141592654

using namespace std;

int main()
{
int x = 14;
double result;

result = atan(x);

cout << "atan(x) = " << result << " radians" << endl;
// Output in degrees
cout << "atan(x) = " << result*180/3.1415 << " degrees" << endl;

return 0;
}``````

When you run the program, the output will be:

```atan(x) = 1.49949 radians
atan(x) = 85.9169 degrees```