Recursive function power(base,exponent)

thulaotzu · #1 09-Nov-2005, 18:12

I have an assignment that I think has some logical errors in the base case and recursive step. My program actually calculates values correctly, but I think it can use some improvements in the logic. Can someone help me fix it so that it will be logically correct?

Here are the instructions given by my instructor:
Write a recursive function power(base,exponent) that, when invoked, returns
base^exponent
For example, power( 3, 4 ) = 3 * 3 * 3 * 3. Assume that exponent is an integer greater than or equal to 1. Hint: The recursion step would use the relationship
base exponent = base · base ^ exponent- 1
and the terminating condition occurs when exponent is equal to 1 because
base^1 = base

Below is my code:

CPP / C++ / C Code:

#include <iostream>

using std::cout;
using std::cin;
using std::endl;


int power (int, int);

int main ()

{
	int base, exp, result;

	//obtain integer from user
	cout<<"Enter the base value: ";
	cin >>base;
	cout<<"Enter the exponent value: ";
	cin>>exp;

	result = power(base, exp);

	cout<<"The result is: "<< result << endl;
	
	return 0;
}


// recursive definition
int power (int base, int exp)
{
	// base case	
	if (exp==1)
		return base * 1;
		
	// recursive step	
	else if (exp >-1)
		exp--;
		
		return base * (power(base,exp));
		
		
}

Paramesh · #2 10-Nov-2005, 07:15

Hi Thu,

Suppose if the user enters 0 as the exponent, the return answer should be 1.
So, here is the modified recursion function:

CPP / C++ / C Code:

int power (int base, int exp)
{
   if(exp >= 1)
       return base * (power(base,exp - 1));

   else
       return 1;
}

The logic is that you must multiply base until exp becomes zero.
i.e:
consider that user enters 3 and 4.
So,

CPP / C++ / C Code:


return base * (power(base,exp - 1));

this line will expand like this:
base * base * base * base * 1

There is one more problem.
What if the user enters negative numbers for the exponent value?
Think about that and add the code for that also.

Regards,

Paramesh.

WaltP · #3 10-Nov-2005, 09:37

Quote:

Originally Posted by Paramesh

Suppose if the user enters 0 as the exponent, the return answer should be 1.

Suppose the reader of posts keep in mind the instructions for the program

Quote:

Originally Posted by thulaotzu

Here are the instructions given by my instructor:
Assume that exponent is an integer greater than or equal to 1.

thulaotzu · #4 10-Nov-2005, 14:53

Paramesh,
it works like a charm!

Thanks, mate.

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Recursive function power(base,exponent)

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