Mathematical Constants in C++

By Animisha Dalal

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 :

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++