# atanh() function in C++ STL

The atanh() is an inbuilt function in C++ STL which returns the inverse hyperbolic tangent of an angle given in radians.

Syntax:

```atanh(data_type x)
```

Parameter: This function accepts one mandatory parameter x which specifies the inverse hyperbolic angle in radian which lies in the range [-1, 1]. The parameter can be of double, float or long double datatype.

Return Value: This function returns the inverse hyperbolic sine of the argument in radians depending on the parameter passed in the argument. The different return values are given in the table below: Below programs illustrate the above method:

Program 1:

 `// C++ program to illustrate ` `// the atanh() function ` `// all return values ` `#include ` `using` `namespace` `std; ` ` `  `int` `main() ` `{ ` `    ``// Return value when -11 ` `    ``x = -2; ` `    ``result = atanh(x); ` ` `  `    ``cout << ``"\natanh(-2) = "` `<< result << ``" radians\n"``; ` `    ``cout << ``"atanh(-2) = "` `<< result * 180 / 3.141592 ` `         ``<< ``" degrees\n"``; ` ` `  `    ``return` `0; ` `} `

Output:

```atanh(0) = 0 radians
atanh(0) = 0 degrees

atanh(-1) = -inf degrees

atanh(1) = inf degrees

atanh(-2) = -nan degrees
```

Errors and Exceptions: The function returns a no matching function error message when a string or any other data_type except the one which the function excepts is passed.

Program 2:

 `// C++ program to demonstrate ` `// the atanh() function  ` `// string passed ` `#include ` `using` `namespace` `std; ` ` `  `int` `main() ` `{ ` `    ``string x = ``"gfg"``; ` ` `  `    ``// Function call to calculate atanh(x) value ` `    ``double` `result = atanh(x); ` ` `  `    ``cout << ``"atanh(50.0) = "` `<< result << ``" radians"` `<< endl; ` `    ``cout << ``"atanh(50.0) = "` `<< result * 180 / 3.141592 ` `         ``<< ``" degrees"` `<< endl; ` `    ``return` `0; ` `} `

Output:

```prog.cpp:11:25: error: no matching function for call to 'atanh(std::__cxx11::string&)'
double result = atanh(x);
```

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