"Not All Control Paths Return a Value"

**EDIT: in addition to the mistakes pointed out below, i was mistakenly trying to compile it as a Win32 project, per this error code

1>MSVCRTD.lib(crtexew.obj) : error LNK2019: unresolved external symbol WinMain@16 >referenced in function __tmainCRTStartup so crisis averted and homework complete. Thank you all very much for your help. hopefully i can similarly pay the community back when i know a thing or two.**

In this assignment we're supposed to use recursion as a technique for determining whether a word qualifies as a palindrome. Although i'm still struggling to become comfortable with it as a problem solving mechanism, this code seems like it should otherwise work. However, the compiler gives me the "not all control paths return a variable" error. Any ideas?

#include<iostream>
#include<fstream>
#include<string开发者_开发百科>
using namespace std;

bool palcheck(string word, int first, int last);

int main()
{
  ofstream palindrome, NOTpalindrome;
  ifstream fin;
  string word;

  palindrome.open("palindrontest.txt");
  NOTpalindrome.open("notPalindronetest.txt");
  fin.open("input5.txt"); //list of palindromes, one per line

  if (palindrome.fail() || NOTpalindrome.fail() || fin.fail())
    return -1;

  while (fin >> word)
  {
    if (palcheck(word, 0, (word.size()-1)) == true)
      palindrome << word << endl;
    else
      NOTpalindrome << word << endl;
  }

  palindrome.close();
  NOTpalindrome.close();
  fin.close();

  return 0;
}

bool palcheck(string word, int first, int last)
{
if (first >= last)
return true;

else if (word[first] == word[last])
return palcheck(word, first+1, last-1);

else// (word[first] != word[last])
return false;

}

---

The error is in your palcheck function. If the expression in the else if was true, the function wouldn't return a value.

The following should fix it:

bool palcheck(string word, int first, int last)
{
  if (first == last)
    return true;

  else if (word[first] == word[last])
    return palcheck(word, first+1, last-1);

  else// ((word[first] != word[last]) || (first > last))
    return false;
}

---

The error is in your palcheck function, you forgot to return the value of the recursed function

bool palcheck(string word, int first, int last)
{
if (first == last)
return true;

else if (word[first] == word[last])
return palcheck(word, first+1, last-1); // <- this return ;)

else// ((word[first] != word[last]) || (first > last))
return false;
}

---

if (first == last)

needs to be

if (first >= last)

in case there are an even number of letters.

---

bool palcheck(string word, int first, int last)
{
if (first == last)
  return true;
else if (word[first] == word[last])
  palcheck(word, first+1, last-1); // <-here
else
  return false;

// <-reaches here
}

The problem is marked here above. When that case is selected, you're not returning anything from the function, which is a problem. You should probably use:

  return palcheck(word, first+1, last-1);