Trouble with finding a vowel using recursion

SnackMan78 · #1 10-May-2005, 05:27

I have a project in which I am to find all of the vowels entered in a word using recursion. I've written something, and based on the displays I have in the code, I am parsing the data properly, but the recursion part is undoing my counts. What do I need to do (and undo) to make this work as intended?

CPP / C++ / C Code:

#include <iostream>
#include <string>
   using namespace std;

int findVowel(string, int, int);
bool vowelSwitch(char chr);

int main()
{
	string inStr;
	bool foundIt = false;
	int cnt = 0, stringLen = 0;

	cout<<"Enter the string to be searched...";
	cin >> inStr;

	stringLen = inStr.size();

	cnt = findVowel(inStr, stringLen - 1, cnt);

	cout<<"\nThe vowel count is: " << cnt;

	cout<< "\n\n";
	return 0;	
}


int findVowel(string inStr, int stringLen, int cnt)
{
	bool itzaVowel = false;
	int dummyVal = 0;

	if(stringLen < 0)
		return cnt;
	else
	{
		char chr = inStr.at(stringLen);
		itzaVowel = vowelSwitch(chr);
		if(itzaVowel)
		{
			cnt++;
			stringLen--;
			dummyVal = findVowel(inStr, stringLen, cnt);
		}
		else
		{
			stringLen--;
			dummyVal = findVowel(inStr, stringLen, cnt);
		}
	}

	cout<<"\nBefore returning, the cnt: " <<  cnt 
		<<", dummyVal = " << dummyVal;
	return cnt;
}


bool vowelSwitch(char chr)
{
	switch(chr)
	{
		case 'A': case 'a':
		case 'E': case 'e':
		case 'I': case 'i':
		case 'O': case 'o':
		case 'U': case 'u':
			cout<<"\nThis character: " << chr << " is a vowel";
			return true;
		default:
			cout<<"\nThis character: " << chr << " is NOT a vowel";
			return false;
	}
}

maprich · #2 12-May-2005, 08:34

Ok firstly: why do you insist doing this with recursion? This kind of problem is far more easily solved by using simple iteration (for(){}).

Secondly To your problem: Your problem lies with variables cnt and dummyVal. Its a bit complicated to explain the reason but here is the correction:

Delete the:

CPP / C++ / C Code:

	int dummyVal = 0;

Replace your 2 instances of:

CPP / C++ / C Code:

	dummyVal = findVowel(inStr, stringLen, cnt);

With:

CPP / C++ / C Code:

	cnt = findVowel(inStr, stringLen, cnt);

this should remedy your problem.

Here's what I think about the reason your original code doesn't work: you count the wovels when the recursion goes "downward" but the information is not passed "upward" and the root of your recursion doesn't get it. Remember that recursion is two way process. By root I mean the point of code that first time calls the recursive function.
Pseudo code:

CPP / C++ / C Code:

let the function be:
F() {
  part A;
  if( go_on ) F();
  part B;
  return sth;
}
now the processing go "downward" until go_on==false :
root =
F() {
    part A;
    if -------------->  F() {
                                part A;
                                if ------------> F() {
                                                      part A;
                                                      ..until go_on==false
from now on the process goes "upward"
                                                      part B;
                                <-------------- return sth;}
                                part B;
    <------------------ return sth;}
    part B;
    return sth;
}

SnackMan78 · #3 12-May-2005, 10:23

Thanks for your help. Your solution worked well.

I agree, using an iterative process like a for/loop would have worked quite well; however, the exercise required using recursion.

Also thanks for your example on the recursion process. I have a couple more problems I need to solve using recursion, so hopefully I can use your example in solving my remaining exercises.

WaltP · #4 12-May-2005, 14:35

Quote:

Originally Posted by maprich

Ok firstly: why do you insist doing this with recursion? This kind of problem is far more easily solved by using simple iteration (for(){}).

Maybe because

Quote:

Originally Posted by SnackMan78

I have a project in which I am to find all of the vowels entered in a word using recursion.

Paraphrased:
I have been given a task requiring me to:
a) find all vowels
b) using recursion
;-) ;-)

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