//-------------------------------------------------------------
// File: writeBackward.cpp
// Name: Sharon M. Tuttle
// last modified: 1-29-05
//
// Contract: writeBackward : string int -> void
//
// Purpose: write the first <charsToWrite> characters in string <str>
//          in reverse order to the screen
//
// preconditions:
//         * charsToWrite <= str.length()
//         * charsToWrite >= 0
//
// postconditions:
//         * the first <charsToWrite> characters in <str> are written
//           in reverse order to the screen, but <str> is unchanged
//
// Examples: for string str1 = "hello there",
//            writeBackward(str1, 11) should cause:
// ereht olleh
//            ...to be written to the screen
//         for string str2 = "",
//            writeBackward(str2, 0) should cause:
//      
//            (nothing; the empty string) to be written to 
//            the screen.
//         for string str3 = "f",
//            writeBackward(str3, 1) should cause:
// f
//            ...to be written to the screen.
//-------------------------------------------------------------

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

void writeBackward (string str, int charsToWrite)
{
    // assertions we can write to verify preconditions
    assert(charsToWrite <= str.length());
    assert(charsToWrite >= 0);

    // base case #1: if no characters to reverse, write nothing
    if (charsToWrite == 0)
    {
        return;
    }

    // base case #2: if 1 character to reverse, simply write
    //    that character
    else if (charsToWrite == 1)
    {
        cout << str[0];
    }

    // recursive case: otherwise, write the last character,
    //    followed by the 1st (charsToWrite-1) characters
    //    written in reverse order
    else
    {
        cout << str[charsToWrite-1];
        writeBackward(str, (charsToWrite-1));
    }
}