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How do you write POWER function?

Jul 1, 2013 at 3:12am
jasonrobertz357 (56)
I just want to see yours to see how stupid my design is :D

below is the example

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???? power(??????????) {
  ???????????????;
}

int main() {
  cout << power(5,4) << endl; //prints 625
  cout << power(5,2) << endl; //prints 25
  cout << power(5,1) << endl; //prints 5
  cout << power(5,0) << endl; //prints 1
  cout << power(5,-1) << endl; //prints 0.2
  cout << power(5,-4) << endl; //prints 0.0016
  return 0;
}
Last edited on Jul 1, 2013 at 3:13am
Jul 1, 2013 at 4:43am
Smac89 (1727)
If your design produces the correct answer, then the only thing it may need is just efficiency. Here is mine:


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unsigned _power( unsigned val, unsigned _pow=0 ) {
	if ( _pow <= 0 )
		return 1;
	return val * _power( val, _pow-1 );
}

int main()
{
	unsigned _pow, _value;
	
	cout << "Enter a value: ";
	cin >> _value;
	cout << "Enter a power: ";
	cin >> _pow;
	cout << _power( _value, _pow ) << endl;
  	
	return 0;
}


Jul 2, 2013 at 6:20am
buffbill (467)
Something like this might serve:

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 double raise(double x,int n)
     {
       assert(x>0);
       double y=1.0;
       for(int i=0;i<n;i++)
       y*=x;
       for(int i=0;i>n;i--)
       y/=x;
       return y;
    }

The problem with this is that power index should be a whole number
unlike pow() which returns a double from two doubles.
btw Smac do you mean this?
if ( _pow <= 0 )
return 1;
Last edited on Jul 2, 2013 at 6:36am
Jul 7, 2013 at 8:09pm
jumper007 (435)
@Smac89:
If your design produces the correct answer, then the only thing it may need is just efficiency.


Actually, using recursion will overload the stack for large values. That's why recursion shouldn't be used only when strictly necessary. However, it's not going to give a longer execution time if the given input consists of low numbers.

In order to make it more efficient I recommend changing the actual recursion with a for loop.

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#include <iostream>

typedef long double ld;

ld power(ld, ld);

int main(int argc, char *argv[]) {
	ld Value, Power;

	std::cout << "Enter a value: ";
	std::cin >> Value;
	std::cout << "Enter a power: ";
	std::cin >> Power;
	std::cout << power(Value, Power) << std::endl;
  	
	system("pause");
	return 0;
}

ld power(ld value, ld power) {
	ld result = 1;

	for (ld i = 0; i < power; ++i) {
		result *= value;
	}

	return (result);
}
Edit & run on cpp.sh


Kind regards,
Raul Butuc
Last edited on Jul 7, 2013 at 8:13pm
Jul 7, 2013 at 9:22pm
Niven (114)
I normally just use the power function included in the math.h header file but if I had to create my own, it would look something like this.

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float Power(float Base, int Power)
{
        float Return = 1;
        if ( Power > 0)
               for (int n = 0; n < Power; n++)
                      Return *= Base;
        else
               for (int n = 0; n > Power; n--)
                      Return /= Base;
        return Return;
}
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