Calculation of power by means of Recursion

Calculation of power by means of Recursion

• Deanrm

  mattii wrote:

  hi, i calculated the power of a number with the help of a recursion: [code] double power(double x, int n) { double product; int count; if (x==0) assert(n>0); if(n >= 0) { product = 1; for (count = 1; count <= n; ++count) product = product * x; return product; } else return 1/power(x, -n); } [/code] But now i want to rewrite this function in order to ensure that the time to computer power(x,n) is only log(n). I think i need to use this formula: x^2n = x^n x^n. But i do not exactly understand how do i have to redefine this function, has anybody here some hints for that... :( matti

  
  
  First thing Array Index always start with 0 .means you can say size of array is 0 to n-1 where n is the total no of argument in your array.so Better if you try to Keep these small thing in your Mind and then Proceed.here is a Small recursive Function to calculate the Power of a Number.
  
  int power(int b,int a)
  {
      static int c=b;
      if(a==1)
          return b;
      else
          return (power((c*b),a-1));
  }
  int main()
  {
  int a =5;
  cout<<power(a,4);
  return 0;
  }
  
  
  Thanx
  
  
  

• n_jagan

  hi,
  
  i develeoped a recursive function for the power
  
  [code]
  double power(double x, int n) {
  if (n < 0)
  return 1/power(x, -n);
  else if (n == 0)
  return 1.0;
  else
  return x * power(x, n-1);
  }
  [/code]
  
  Has this function now already a runtime of log(n), because i thought i have to use this formula x^2n = x^n x^n in any way...
  
  matti
  
  

• KeithCourage

  Hello,

  You could use pow function instead of writting your own ;)

  Otherwise you could do something like

  
  bool isOdd = false;
  if (1 == n%2)
  {
  isOdd = true;
  }
  for(int i=0; i<(isOdd (n-1/2):n/2;i++)
  {
  product = product*x;
  }
  product = product*product;
  if (isOdd)
  product=product*x;
  

  Richard

  
  
• Calculation of power by means of Recursion