Bdtjtk

I am self-teaching myself data-structures using Malik's "Data Structures and Algorithm Desgin using c++". The first exercise is to make an object of type numeralType and encapsulate in it all the necessary operations to take in a string a return its value in the roman numeral system.

DISCALIMER 1: Please assume that there is data validation and everything is done except the function that converts the string into its value in the roman numeral system. Also, I am using VS17.

I will not post the original "conversion" function. Instead, I will post a generic version of the algorithm used in the function.

here it is:

#include <iostream>

#include <string>

#include<map>





int main()

{

int result = 0;

std::map<char, int> charMap = { {'f',1},{'h',2},{'x',3},{'b',4},{'l',5} };

std::string testString = "lbxhf";

for (unsigned int i = 0; i < testString.length(); i++)

    {

        if (charMap.at(testString.at(i)) >= charMap.at(testString.at(i + 1)))

            result = charMap.at(testString.at(i)) + 

charMap.at(testString.at(i + 1));

    }

system("pause");

return 0;

}

This code automatically calls abort() but compiles fine.

Using VS's debugger, i have singled out that the cause is string based, but I don't know exactly why.

Using a try/catch block I get that an invalid string position error. Here is the try/catch version:

int main()

{

    int result = 0;

    std::map<char, int> charMap = { {'f',1},{'h',2},{'x',3},{'b',4},{'l',5} };

    std::string testString = "lbxhf";



    try

    {



        for (unsigned int i = 0; i < testString.length(); i++)

        {

            if (charMap.at(testString.at(i)) >= charMap.at(testString.at(i + 1)))

                result = charMap.at(testString.at(i)) + charMap.at(testString.at(i + 1));

        }

    }

    catch(const std::out_of_range& e) 

    {

        std::cout << e.what() << std::endl;

    }



    system("pause");

    return 0;

}

I have been scratching my head around this for a whole day now and would like a few tips on how to solve this problem.

Again, this is a generic version of an algorithm that takes in a string of roman numerals and returns it value as an integer.

DISCLAIMER 2: This algorithm implies addition only, based on the rules of addition/subtraction of the roman numeral system.
DISCALIMER 3: it is important to me that I use std::map, I know it can be done using an array/vector type, but I also wish to practice using stl containers.

Thank you in advance (no need to be terribly mean guys!!)

You are accessing testString.at(i + 1), but i may be up to testString.length()-1 because of the loop condition

for (unsigned int i = 0; i < testString.length(); i++)

This is the reason for the out-of-bounds exception. (testString.length()-1 is the last index of testString and going one higher will be out-of-bounds.)

Not sure about your intentions, but maybe you want the loop condition to be

for (unsigned int i = 0; i+1 < testString.length(); i++)

to only compare neighboring elements of the string.

Here's what I came up with to solve the problem and achieve my goal:

#include<iostream>

#include<string>

#include<map>





int main()

{



    int result = 0;

    std::map<char, int> charMap = { {'f',1},{'h',2},{'x',3},{'b',4},{'l',5} };

    std::string testString("lbxhf");

    char lastChar = testString.back();

    for (unsigned int i = 0; i+1 < testString.length(); i++)

    {

        if(charMap.at(testString.at(i)) >= charMap.at(testString.at(i+1)))

            result += charMap.at(testString.at(i));

    }

    result += charMap.at(lastChar);

    printf("%in", result);

    system("pause");

    return 0;

}