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What is atan() in C++ ?

Sheza Naveed

The atan() function returns the inverse tangent of a number. Figure 1 shows the C++ representation of the mathematical expression.

Figure 1: C++ representation of the mathematical expression

To use the atan() function, the cmath header file needs to be included in the program, as shown below:

#include <cmath>


It takes a single number as an argument that can be positive, negative, or zero. This value can be a float, double or long double.

Return value

It returns a single value of an angle in radians, ranging from ‘-π/2’ to ‘π/2’. This value can be a float, double, or long double:

double atan(double x);
float atan(float x);
long double atan(long double x);


The following code explains the use of atan() function in C++. It returns the angle value in radians by default. This value can be converted to degrees, as shown:

#include <iostream>
#include <cmath>
using namespace std;

int main() {
  double input = 57.6;
  double resultRadians = atan(input);
  double resultDegrees = (resultRadians * 180) / M_PI;
  //M_PI gives the value of Pi in C++ and is defined in the cmath library
  cout << "atan(50.6) = " << resultRadians << " radians" << endl;
  cout << "atan(50.6) = " << resultDegrees << " degrees" << endl;

  return 0;




Sheza Naveed
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