help in c++ recursive functions

vinch · #1 13-Jul-2005, 07:19

had an assignment where in i have to create a recursive function program
given a base number and an exponent.

for example: power(10,2)= 100

10 is the base and 2 is the exponent;

here's what ive done so far:

CPP / C++ / C Code:

#include <iostream.h>

int power(int base, int exponent);
int value;
main(void)
{	int b,e;
	cout<<"Enter base number:";cin>>b;
	cout<<"Enter exponent:";cin>>e;
	power(b,e);
	cout<<value;
	return 0;
}

power(int base, int exponent)
{
	int value;
	value=power(base*base,exponent);
	return (value);
}

pls. help me locate the error in the code. your help will be much appreciated. thanx in advance!!!

Dave Sinkula · #2 13-Jul-2005, 08:13

Recursion can be viewed as an alternate form of a loop. Just like a loop needs a terminating condition, so does the recursion. Each time you recurse, the function should be passed a value that converges to this condition (for example, a base that is successively one less than the previous and a check for a base that is greater than zero).

On your next spin, it might be good to use standard C++ (not pre-standard <iostream.h> headers, for example). And an implicitly declared main is over a decade out of date as well. And you don't need to use a global variable.

QED · #3 13-Jul-2005, 08:31

Quote:

Originally Posted by vinch

CPP / C++ / C Code:

power(int base, int exponent)
{
	int value;
	value=power(base*base,exponent);
	return (value);
}

Under what condition will your recursive function stop and finally return a value? You have written an infinitely recursing function. Once we enter power, we call power again; and in there, we call power again; and in there... forever! The key step when using recursion is to have some terminal condition (no, not an illess

) which controls when to stop recursing. For example,

CPP / C++ / C Code:

int eliminateFactor(int val, int factor)
{
  if (val % factor > 0) { // this is the terminal condition
    return val;     // see, we don't recurse in this case
  }

  val = val / factor;

  return eliminateFactor(val, factor);  // here, we recurse
}

Try rethinking your function and determine what will be the terminal condition(s), and how exactly to recurse. Then post any further questions/problems if they arise.

Hope this helps.

Matthew

Edit: Oops, I am rather late!

p_kumar811 · #4 13-Jul-2005, 10:40

Hi,
I just saw your code and was wondering on 2 count.
1) In the code for you power fuction will go on an infinite loop as there is no Exit condition.
2) In your main function you are not capturing the value that is being returned by the main function. You need to capture the value that is being returned by the function. And also the concept of using Global varaibles is a old concept and is not a good Object Orientation Practise.

The following code should work:

CPP / C++ / C Code:

#include <iostream>

using namespace std;

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

void main()
{
	int base, exp, value;
	cout<<"Enter the Base Value: ";
	cin >>base;
	cout<<"Enter The Exponent Value: ";
	cin>>exp;
	value = power(base, exp);
	cout<<"The value is: "<<value;
}

This has been tested in VC++ Compiler. and i guess this shld work in all Windows based Compilers.

Regards

Prasanth

vinch · #5 15-Jul-2005, 06:55

Quote:

Originally Posted by p_kumar811

Hi,
I just saw your code and was wondering on 2 count.
1) In the code for you power fuction will go on an infinite loop as there is no Exit condition.
2) In your main function you are not capturing the value that is being returned by the main function. You need to capture the value that is being returned by the function. And also the concept of using Global varaibles is a old concept and is not a good Object Orientation Practise.

The following code should work:

CPP / C++ / C Code:

#include <iostream>

using namespace std;

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

void main()
{
	int base, exp, value;
	cout<<"Enter the Base Value: ";
	cin >>base;
	cout<<"Enter The Exponent Value: ";
	cin>>exp;
	value = power(base, exp);
	cout<<"The value is: "<<value;
}

This has been tested in VC++ Compiler. and i guess this shld work in all Windows based Compilers.

Regards

Prasanth

thanx p_kumar811 for the help!!

luaik · #6 04-Jan-2006, 05:52

i should make a recursive programm
that print the partition of the number N
that's mean
for N=4
4
31
22
211
1111
if N=5
5
41
32
311
221
2111
11111

if N=6
6
51
42
411
33
321
3111
222
2211
21111
111111

davekw7x · #7 04-Jan-2006, 09:50

Quote:

Originally Posted by p_kumar811

Hi,

CPP / C++ / C Code:


void main()

This has been tested in VC++ Compiler. and i guess this shld work in all Windows based Compilers.

Gives an error for Cygwin g++ (on Windows XP) and, therefore, will not compile:

Code:

15: error: `main' must return `int'

Regards,

Dave

Guidelines Plz · #8 04-Jan-2006, 12:22

Welcome luaik.

First of all, why would you want to post a reply to a very old thread rather than start a new thread for your problem?

Second:

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help in c++ recursive functions

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