c++ programming iteration and recursion - c++

Question

I am looking for some quick tips on a homework assignment. We are given a few problems and have to write two quick programs on how to solve the problems with one each of iteration and recursion. I'm sure this is easier than I think, but I am getting easily confused over the two. By no means do I want anyone to fully solve the problems for me, I won't learn anything! But if you could look at what I have so far and let me know if I am heading in the right direction. Also, the code does not need to compile, our professor wants us to have a general idea of the differences of iteration vs. recursion.
Problem: check a string to see if it is a palindrome.
My solution- I think it is the iterative solution:
bool iterative_palindrome (const string& str) {
string line, result;
stack <char> stack_input;
//user enters string, program takes it
cout << "Enter string: " << endl;
while (getline (cin, line) && (line != "")) {
//push string into stack
for (size_t i = 0; i < line.size(); i++) {
stack_input.push(line[i]);
//create reverse of original string
while (!stack_input.empty()) {
result += stack_input.top();
stack_input.pop();
return result;
}
//check for palindrome, empty string
if (line == result || line = "0" || line.empty()) {
return true;
cout << line << " is a palindrome!" << endl;
} else {
return false;
cout << line << " is NOT a palindrome." << endl;
cout << "Enter new string: " << endl;
}
}
}
}
I remind everyone, I am pretty new to this stuff. I've read a few things already, but am still having a hard time wrapping my head around this.

Answer 1

Here's the general idea:
Iterative:
Initialize two pointers one pointer to the start and end of the string.
Compare the characters pointed, if different -> not palindrome.
Increase the start pointer and decrease the end pointer.
Repeat until start pointer >= end pointer.
Recursive (more difficult than iterative in this case):
End condition: A string of length zero or one is a palindrome.
A string is a palindrome if the first and last characters are the same and if the string without the first and last characters is a palindrome.
You can implement this recursive algorithm more efficiently by passing pointers to the first and last character in the string instead of copying the string between recursions.
Hope this helps :-)

Answer 2

I figure writing code is the best way to explain the two approaches. Is this code understandable?
bool iterative_palindrome(const string& str) {
int size = str.size();
for (int i=0; i<str.size()/2; i++) {
if (str[i] != str[size-i-1])
return false;
}
return true;
}
You call this like recursive_palindrome(str, 0).
bool recursive_palindrome(const string& str, int index) {
int size = str.size();
if (index >= size/2)
return true;
if (str[index] == str[size-index-1])
recursive_palindrome(str, index+1);
else
return false;
}