# atan2() function in C++ STL

The atan2() is an inbuilt function in C++ STL which returns tangent inverse of (y/x), where y is the proportion of the y-coordinate and x is the proportion of the x-coordinate. The numeric value lies between – and representing the angle of a (x, y) point and positive x-axis. It is the counterclockwise angle, measured in radian, between the positive X-axis, and the point (x, y).

Syntax:

atan2(data_type y, data_type x)


Parameters:The function accepts two mandatory parameters which are decribed below:

• y – This value specifies y-coordinate.
• x – This value specifies the x-coordinate.

The parameters can be of double, float or long double datatype.

Return Value: The function returns a numeric value between – and representing the angle of a (x, y) point and positive x-axis. It is the counterclockwise angle, measured in radian, between the positive X-axis, and the point (x, y).

Below programs illustrate the atan2() function:

Program 1:

 // CPP program to demonstrate the atan2()  // function when both parameters are of  // same type  #include  using namespace std;     int main()  {      double x = 10.0, y = 10.0, result;      result = atan2(y, x);         cout << "atan2(y/x) = " << result           << " radians" << endl;      cout << "atan2(y/x) = " << result * 180 / 3.141592           << " degrees" << endl;         return 0;  }

Output:

atan2(y/x) = 0.785398 radians
atan2(y/x) = 45 degrees


Program 2:

 // CPP program to demonstrate the atan2()  // function when both parameters are of  // different types  #include  using namespace std;     int main()  {      double result;      float x = -10.0;      int y = 10;      result = atan2(y, x);         cout << "atan2(y/x) = " << result           << " radians" << endl;      cout << "atan2(y/x) = " << result * 180 / 3.141592 << " degrees" << endl;         return 0;  }

Output:

atan2(y/x) = 2.35619 radians
atan2(y/x) = 135 degrees


Program 3:

 // CPP program to demonstrate the atan2()  // function when y/x is undefined  #include  using namespace std;     int main()  {      double x = 0.0, y = 10.0, result;      result = atan2(y, x);         cout << "atan2(y/x) = " << result           << " radians" << endl;      cout << "atan2(y/x) = " << result * 180 / 3.141592           << " degrees" << endl;         return 0;  }

Output:

atan2(y/x) = 1.5708 radians
atan2(y/x) = 90 degrees


Program 4:

 // CPP program to demonstrate the atan2()  // function when both parameters are zero  #include  using namespace std;     int main()  {      double x = 0.0, y = 0.0, result;      result = atan2(y, x);         cout << "atan2(y/x) = " << result           << " radians" << endl;      cout << "atan2(y/x) = " << result * 180 / 3.141592           << " degrees" << endl;         return 0;  }

Output:

atan2(y/x) = 0 radians
atan2(y/x) = 0 degrees


Errors and Exceptions: The function returns no matching function for call to error when a string or character is passed as an argument.
Program 5:

 // CPP program to demonstrate the atan2()  // errors and exceptions  #include  using namespace std;     int main()  {      double x = 0.0, y = 10.0, result;      result = atan2("1", x);         cout << "atan2(y/x) = " << result << " radians" << endl;         cout << "atan2(y/x) = " << result * 180 / 3.141592           << " degrees" << endl;         return 0;  }

Output:

prog.cpp:9:26: error: no matching function for call to 'atan2(const char [2], double&)'
result = atan2("1", x);

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