(C++) Calculating the factorial

• A plain function
• A recursive function
• A template metaprogram

plain function

include <cassert>


int Factorial(const int n)
{
  assert(n>=0);
  int result = 1;
  for (int i=1; i<=n; ++i)
  {
    result*=i;
  }
  return result;
}
int main()
{
  assert(Factorial(0)==1);
  assert(Factorial(1)==1);
  assert(Factorial(2)==2);
  assert(Factorial(3)==6);
  assert(Factorial(4)==24);
  assert(Factorial(5)==120);
}

recursive function

include <cassert>


//The common recursive function
int Factorial(const int n)
{
  assert(n >= 0);
  if (n==0) return 1;
  return (n * Factorial(n-1));
}
int main()
{
  assert(Factorial(0)==1);
  assert(Factorial(1)==1);
  assert(Factorial(2)==2);
  assert(Factorial(3)==6);
  assert(Factorial(4)==24);
  assert(Factorial(5)==120);
}

template metaprogram

//The compile-time assert
template <bool>
struct CtAssert;
template <>
struct CtAssert<true> {};
//The template metaprogram for factorial
template <unsigned int N>
struct factorial
{
  static unsigned const value = N * factorial<N-1>::value;
};
template <>
struct factorial<0>
{
  static unsigned const value = 1;
};
int main()
{
  CtAssert<(factorial<0>::value==1)>();
  CtAssert<(factorial<1>::value==1)>();
  CtAssert<(factorial<2>::value==2)>();
  CtAssert<(factorial<3>::value==6)>();
  CtAssert<(factorial<4>::value==24)>();
  CtAssert<(factorial<5>::value==120)>();
}

Code links

• assert
• cassert (header file)
• cout
• endl
• for
• int
• main
• std
• struct
• std::cout
• std::endl
• template
• unsigned