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 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
#include<bits/stdc++.h>
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

// CPP program to demonstrate the atan2()
// function when both parameters are of
// different types
#include <bits/stdc++.h>
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
#include<bits/stdc++.h>
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

// CPP program to demonstrate the atan2()
// function when both parameters are zero
#include<bits/stdc++.h>
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

// CPP program to demonstrate the atan2()
// errors and exceptions
#include<bits/stdc++.h>
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);