 # C atan2()

The atan2() function computes the arc tangent of an argument.

## C atan2() Prototype

`double atan2(double y, double x);`

Function atan2() takes two arguments: x-coordinate and y-coordinate, and calculate the angle in radians for the quadrant.

For better understanding of atan2():

`[Mathematics] tan-1(y/x) = atan2(y,x) [In C programming] `

Two other functions atan2f() and atan2l() are also present in C to specifically work with `float` and `long double` respectively.

The `atan2()` function is defined in <math.h> header file.

## C atan2() range

The arguments of atan2() can be any number, either positive or negative.

## Example: C atan2() function

``````#include <stdio.h>
#include <math.h>
#define PI 3.141592654

int main()
{
double x, y, result;
y = 2.53;
x = -10.2;
result = atan2(y, x);
result = result * 180.0/PI;

printf("Tangent inverse for(x = %.1lf, y = %.1lf) is %.1lf degrees.", x, y, result);
return 0;
}
``````

Output

```Tangent inverse for(x = -10.2, y = 2.53) is 166.1 degrees.
```

### Caution while using atan2()

The value of second argument passed should not be 0. If the second argument passed is 0, the program will not run correctly.