A little-known feature of C++ is that the `cmath`

library actually provides many mathematical constants that you can make use of in your quantitative finance programs.

To include the mathematical constants, you need to use a `#define`

macro called `_USE_MATH_DEFINES`

and add it before importing the `cmath`

library:

```
#define _USE_MATH_DEFINES
#include <cmath>
#include <iostream>
int main() {
std::cout << M_PI << " " << M_E << " " << M_SQRT2 << endl;
return 0;
}
```

There are quite a few constants on offer. See if you can spot the ones that will be useful in quantitative finance:

Mathematical Expression | C++ Symbol | Decimal Representation |
---|---|---|

pi | M_PI | 3.14159265358979323846 |

pi/2 | M_PI_2 | 1.57079632679489661923 |

pi/4 | M_PI_4 | 0.785398163397448309616 |

1/pi | M_1_PI | 0.318309886183790671538 |

2/pi | M_2_PI | 0.636619772367581343076 |

2/sqrt(pi) | M_2_SQRTPI | 1.12837916709551257390 |

sqrt(2) | M_SQRT2 | 1.41421356237309504880 |

1/sqrt(2) | M_SQRT1_2 | 0.707106781186547524401 |

e | M_E | 2.71828182845904523536 |

log_2(e) | M_LOG2E | 1.44269504088896340736 |

log_10(e) | M_LOG10E | 0.434294481903251827651 |

log_e(2) | M_LN2 | 0.693147180559945309417 |

log_e(10) | M_LN10 | 2.30258509299404568402 |

Note that it is not best practice within C++ to use #defines for mathematical constants! Instead, as an example, you should use `const double pi = 3.14159265358979323846;`

. The #defines are a legacy feature of C.