# C atan2()

The atan2() function defined in the math.h header file. It helps to return the arc tangent value of the given number in radians. This function takes two arguments 'x-coordinate' and 'y-coordinate' and determines the correct quadrant based on the signs of both values.

``````
double atan2(double y, double x); #where x &y are floating point values
```
```

Also, two functions atan2f() and atan2l() were used with type float and long double respectively.

``````
float atan2f(float y,float x);
long double atan2l(long double y,long double x);
```
```

## atan2() Parameters:

The atan2() function takes two parameters and it should be any number, either positive or negative.

Parameter Description Required / Optional
x floating-point value representing an x-  coordinate  Required
y      floating-point value representing a y-coordinate Required

## atan2() Return Value

The return value of atan2() function is a number in the interval [-pi,+pi] in radians.

Input Return Value
any positive or negative number a number in the interval [-pi,+pi]

## Examples of atan2()

### Example 1: Working of atan2() function in C?

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

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

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

Output:

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

### Example 2: How atan2() function worked in C?

``````
#include <stdio.h>
#include <math.h>
#define PI 3.14159265

int main () {
double x, y, out, value;

x = -7.0;
y = 7.0;
value = 180.0 / PI;

out = atan2 (y,x) * value;
printf("Arc tangent of x = %lf, y = %lf ", x, y);
printf("is %lf degrees\n", out);

return(0);
}
```
```

Output:

```
Arc tangent of x = -7.000000, y = 7.000000 is 135.000000 degrees
```
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