The **#key# `atan()` function:  also called the `arc tangent` function #key#** returns the inverse tangent of a number. To be more specific, it returns the inverse tangent of a number in  radians.

Figure 1 shows the *mathematical representation* of the `atan()` function and Figure 2 shows the *visual representation* of the `atan()` function.

> Note: The `math.h` header file is required for this function.

To convert `radians` to `degrees`, use the following formula.
```c
degrees = radians * ( 180.0 / PI )
```

# Syntax
```c
double atan(double num)
```
# Parameter
This function requires a number as a parameter. The parameter must be a double value between -1 and 1.
- -1 <= parameter <= 1 

# Return value
`atan()` returns the `inverse tangent` of a number (radian double value) that is sent as a parameter. The return value lies in interval `[-pi/2,pi/2]` radians.

# Example


#include<stdio.h>
//header file
#include<math.h>

int main() {
    //positive number in radians
    printf("The arc tangent of %lf is %lf radians \n", 0.5, atan(0.5));

    // negative number in radians
    printf("The arc tangent of %lf is %lf radians \n", -0.5, atan(-0.5));

    //applying atan() and then converting the result in radians to degrees
    // radians = 1.0
    // PI = 3.14159265
    double result=atan(1.0) * (180.0 / 3.14159265);
    printf("The arc tangent of %lf is %lf degrees \n", 1.0, result);


}

What is atan() in C?

Returns the inverse tangent of a number in radians. Requires a -1 to 1 double value.