recursion help

[timebetold]

I have a program do soon and I can get the function to work but I can't get it to work as a recursive function. The green(code after the slash marks) is my attempt at recursion but it doesn't work. This is what I have:

#include<iostream>
#include<cmath>
 
using namespace std;
 
double power(double b, double p);
 
 
void main()
{
    cout << "Programmed by Heather Fischer\n";
 
    double answer;
    cout.setf(ios::fixed);
    cout.precision(0);
    answer = power (2,32);
    cout << answer << endl;
    answer = power(3,5);
    cout << answer << endl;
    answer = power(2,15);
    cout << answer << endl;
 
 
}
double power(double b, double p)
{
    double answer;
    if ( static_cast<int>(p) % 2 == 0)                        
    {
        //answer = power(b*b,p/2);                          
        answer = pow(pow(b,2.0),(p/2.0));
    }
    else                                
    {                                 
        //answer = b * power(b*b,(p-1)/2);                     
        answer = b * pow(pow(b,2.0),((p-1)/2.0));   
    }
    return answer;
}    

what am i doing wrong?

[AdrianH]

I have a program do soon and I can get the function to work but I can't get it to work as a recursive function. The green(code after the slash marks) is my attempt at recursion but it doesn't work. This is what I have:

#include<iostream>
#include<cmath>
 
using namespace std;
 
double power(double b, double p);
 
 
void main()
{
    cout << "Programmed by Heather Fischer\n";
 
    double answer;
    cout.setf(ios::fixed);
    cout.precision(0);
    answer = power (2,32);
    cout << answer << endl;
    answer = power(3,5);
    cout << answer << endl;
    answer = power(2,15);
    cout << answer << endl;
 
 
}
double power(double b, double p)
{
    double answer;
    if ( static_cast<int>(p) % 2 == 0)                        
    {
        //answer = power(b*b,p/2);                          
        answer = pow(pow(b,2.0),(p/2.0));
    }
    else                                
    {                                 
        //answer = b * power(b*b,(p-1)/2);                     
        answer = b * pow(pow(b,2.0),((p-1)/2.0));   
    }
    return answer;
}    

what am i doing wrong?

Try expanding:

power(2,32)
=power((2)*(2),16)
=power((2*2)*(2*2),8)
=power((2*2*2*2)*(2*2*2*2),4)
=power((2*2*2*2*2*2*2*2)*(2*2*2*2*2*2*2*2),2)
=power((2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2)*( 2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2),1)
=power((2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2* 2*2*2*2*2*2*2*2*2*2*2)*(2*2*2*2*2*2*2*2*2*2*2*2*2* 2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2),0)
=power((2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2* 2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2* 2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2)*(2*2*2*2*2*2* 2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2* 2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2* 2*2*2*2*2*2*2*2),0)
…

As you can see, this recursive function will never stop because 0%2 = 0

Hope that helps.


Adrian

[timebetold]

I figured it out. If anyone is interested here is my code:

#include<iostream>
#include<cmath>

using namespace std;

double power(double b, double p);


void main()
{
cout << "Programmed by Heather Fischer\n\n";
double b =0, p=0;
double answer;
cout.setf(ios::fixed);
cout.precision(0);
answer = power (2,32);
cout << " 2 ^ 32 = " << answer << endl;
answer = power(3,3);
cout << " 3 ^ 3 = " << answer << endl;
answer = power(2,15);
cout << " 2 ^ 15 = " << answer << endl << endl;


}
double power(double b, double p)
{
double answer;
if (p == 0)
{
return 1;
}
else if ( static_cast<int>(p) % 2 == 0)
{

answer = power(b*b,p/2);
//answer = pow(pow(b,2.0),(p/2.0));
}
else
{
answer = b * power(b*b,(p-1)/2);
//answer = b * pow(pow(b,2.0),((p-1)/2.0));
}
return answer;
}

[AdrianH]

Great stuff.


Adrian