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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 described 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

 // CPP program to demonstrate the atan2()// function when both parameters are of// same type#includeusing 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

 // 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

 // CPP program to demonstrate the atan2()// function when y/x is undefined#includeusing 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

 // CPP program to demonstrate the atan2()// function when both parameters are zero#includeusing 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

 // CPP program to demonstrate the atan2()// errors and exceptions#includeusing 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 , double&)'
result = atan2("1", x);

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