Write a recursive function that reverses the input string

I'll instead explain the recursive algorithm itself. Take the example "input" which should produce "tupni". You can reverse the string recursively by

• If the string is empty or a single character, return it unchanged.
• Otherwise,
  1. Remove the first character.
  2. Reverse the remaining string.
  3. Add the first character above to the reversed string.
  4. Return the new string.

Try this one

string reverse(string &s)
{
    if( s.length() == 0 )  // end condtion to stop recursion
        return "";

    string last(1,s[s.length()-1]);  // create string with last character
    string reversed = reverse(s.substr(0,s.length()-1));
    return last+reversed; // Make he last character first
}

A recursive function must have the following properties

• It must call itself again
• It must have a condition when the recursion ends. Otherwise you have a function which will cause a stack overflow.

This recursive function does basically create a string of the last character and then call itself again with the rest of the string excluding the last character. The real switching happens at the last line where last+reversed is returned. If it would be the other way around nothing would happen.

It is very inefficient but it works to show the concept.

Just to suggest a better way of handling recursion:

String reversal using recursion in C++:

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

string reverseStringRecursively(string str){
    if (str.length() == 1) {
        return str;
    }else{
        return reverseStringRecursively(str.substr(1,str.length())) + str.at(0);
    }
}

int main()
{
    string str;
    cout<<"Enter the string to reverse : ";
    cin>>str;

    cout<<"The reversed string is : "<<reverseStringRecursively(str);
    return 0;
}

I won't write a full-blown algorithm for you, but here's a hint:

How about swapping the two outermost characters, and then apply the same to the characters in the middle?

Oh, and if that book really proposed string reverse(string str) as an appropriate function signature for this, throw it away and buy a good book instead.