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# atan() function for complex number in C++

• Last Updated : 17 Aug, 2022

The atan() function for complex numbers is defined in the complex header file. This function is the complex version of the atan() function. This function is used to calculate the complex arc tangent of complex number z and returns the arc tangent of complex number z.

Syntax:

```template<class T> complex<T>
atan (const complex<T>& z );```

Parameter: This method takes a mandatory parameter z which represents the complex number.

Return value: This function returns the arc tangent of complex number z. Below programs illustrate the atan() function in C++:

Example 1:

## cpp

 `// c++ program to demonstrate` `// example of atan() function.`   `#include& lt; bits / stdc++.h & gt;` `using` `namespace` `std;`   `// driver program` `int` `main()` `{` `    ``complex& lt;` `    ``double``& gt;` `    ``complexnumber(-2.0, 0.0);`   `    ``// use of atan() function for complex number` `    ``cout& lt;` `    ``<` `    ``"` `    ``The ``atan` `of& quot;` `    ``<` `    ``<` `    ``complexnumber& lt;` `    ``<` `    ``"` `    ``is& quot;` `    ``<` `    ``<` `    ``atan``(complexnumber) & lt;` `    ``<` `    ``endl;`   `    ``return` `0;` `}`

Output:

`The atan of (-2,0) is (-1.10715,0)`

Time Complexity: O(1)
Auxiliary Space: O(1)

Example 2:

## cpp

 `// C++ program to demonstrate` `// example of atan() function.`   `#include& lt; bits / stdc++.h & gt;` `using` `namespace` `std;`   `// driver program` `int` `main()` `{` `    ``complex& lt;` `    ``double``& gt;` `    ``complexnumber(0.0, 2.0);`   `    ``// use of atan() function for complex number` `    ``cout& lt;` `    ``<` `    ``"` `    ``The ``atan` `of& quot;` `    ``<` `    ``<` `    ``complexnumber& lt;` `    ``<` `    ``"` `    ``is& quot;` `    ``<` `    ``<` `    ``atan``(complexnumber) & lt;` `    ``<` `    ``endl;`   `    ``return` `0;` `}`

Output:

`The atan of (0,2) is (1.5708,0.549306)`

Time Complexity: O(1)
Auxiliary Space: O(1)

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