Mathematical Constants in C++

In this tutorial, we will learn how to use the mathematical constants in C++.

We use mathematical constants in various places from simple mathematical calculations to physics to chemistry and even financial problems. C++ has a few predefined constants in its math library which we can use to access the values wherever needed in our program.

We use the following header file :

#define _USE_MATH_DEFINES
#include <cmath>

Here, _USE_MATH_DEFINES is a #define macro. C++ has the following constants with their values :

Symbol	Expression	Value
M_E	e	2.71828182845904523536
M_LOG2E	log2(e)	1.44269504088896340736
M_LOG10E	log10(e)	0.434294481903251827651
M_LN2	ln(2)	0.693147180559945309417
M_LN10	ln(10)	2.30258509299404568402
M_PI	pi	3.14159265358979323846
M_PI_2	pi/2	1.57079632679489661923
M_PI_4	pi/4	0.785398163397448309616
M_1_PI	1/pi	0.318309886183790671538
M_2_PI	2/pi	0.636619772367581343076
M_2_SQRTPI	2/sqrt(pi)	1.12837916709551257390
M_SQRT2	sqrt(2)	1.41421356237309504880
M_SQRT1_2	1/sqrt(2)	0.707106781186547524401

 

Here I have written a simple program to access the values :

Program to show Mathematical Constants in C++ :

#define _USE_MATH_DEFINES
#include<cmath>
#include<iostream>
using namespace std;
int main()
{
  cout << "log10(e) = " << M_LOG10E<< endl << "exp = " << M_E << endl << "sqrt(2) = " << M_SQRT2 << endl;
  return 0;
}

Output :

log10(e) = 0.434294
exp = 2.71828
sqrt(2) = 1.41421

Now, we write another program to find the area of a circle using M_PI constant.

Program to find the area using M_PI :

#define _USE_MATH_DEFINES
#include<cmath>
#include<iostream>
using namespace std;
int main()
{
  int r;
  float a;
  cout << "Enter the value of radius : ";
  cin >> r;
  a = M_PI * r * r ;
  cout << "area of the circle is : " << a << endl;
  return 0;
}

Output :

Enter the value of radius : 9
area of the circle is : 254.469

Hope this was helpful. Enjoy Coding!

Also read :

PI constant in C++

Vector erase() and clear() in C++