满足中断条件后循环继续

Question

My current assignment requires me to allow for a user to pass strings of characters and convert from roman numerals to a decimal value. I've faced an issue that when random words are passed through the program it must return the longest valid prefix and ignore the remaining characters. My code runs through a while loop and once it reaches the break condition it repeats the code again for the remaining characters. I'm unsure what next step I should take to fix this code to output correctly. Following image shows the characters to pass through the code. Image of test failure

#include <iostream>
#include <ctype.h>

using namespace std;
int
main (){
   while (!cin.eof ()){
    char inputChar;
    int result = 0;
    while (cin.get (inputChar))
    {
        inputChar = toupper (inputChar);
        if (inputChar == 'M')
            result = result + 1000;
        else if (inputChar == 'D')
        {
            inputChar = cin.peek ();
            inputChar = toupper (inputChar);
            if (inputChar == 'M')
            {
                result = result - 500;
                continue;
            }
            else if (inputChar == 'D'){
                result = result;
                continue;
            }
            else
            {
                result = result + 500;
                continue;
            }
        }
        else if (inputChar == 'C')
        {
            inputChar = cin.peek ();
            inputChar = toupper (inputChar);
            if (inputChar == 'M' || inputChar == 'D')
            {
                result = result - 100;
                continue;
            }
            else
            {
                result = result + 100;
                continue;
            }
        }
        else if (inputChar == 'L')
        {
            inputChar = cin.peek ();
            inputChar = toupper (inputChar);
            if (inputChar == 'M' || inputChar == 'D' || inputChar == 'C')
            {
                result = result - 50;
                continue;
            }
            else
            {
                result = result + 50;
                continue;
            }
        }
        else if (inputChar == 'X')
        {
            inputChar = cin.peek ();
            inputChar = toupper (inputChar);
            if (inputChar == 'M' || inputChar == 'D' || inputChar == 'C'
                || inputChar == 'L')
            {
                result = result - 10;
                continue;
            }
            else
            {
                result = result + 10;
                continue;
            }
        }
        else if (inputChar == 'V')
        {
            inputChar = cin.peek ();
            inputChar = toupper (inputChar);
            if (inputChar == 'M' || inputChar == 'D' || inputChar == 'C'
                || inputChar == 'L' || inputChar == 'X')
            {
                result = result - 5;
                continue;
            }
            else
            {
                result = result + 5;
                continue;
            }
        }
        else if (inputChar == 'I')
        {
            inputChar = cin.peek ();
            inputChar = toupper (inputChar);
            if (inputChar == 'M' || inputChar == 'D' || inputChar == 'C'
                || inputChar == 'L' || inputChar == 'X' || inputChar == 'V')
            {
                result = result - 1;
                continue;
            }
            else
            {
                result = result + 1;
                continue;
            }
        }
        else{
            break;
        }
    }
    if (result != 0)
    {
        cout << result << endl;
    }
}
return 0;
}

Answer 1

Your break statement does not go out of the both while loops. It only breaks the inner loop, not the outer one. You can use a flag to tell the outer loop not to continue:

int main() 
{
   bool exit_loop = false; // define a flag here
   while (!cin.eof()) {
      char inputChar;
      int result = 0;
      if (exit_loop) // check the flag here
         break;
      while (cin.get(inputChar))
      {

and while breaking set the flat to true:

 }
 else 
 {
    exit_loop = true; // set the flag here
    break;
 }

Answer 2

Maybe try clearing the buffer at the end of the outer loop. This way the longest prefix is printed and the same word isn't being used again through the iteration.

    if (result != 0)
    {
        cout << result << endl;
    }
    cin. ignore(10000, '\n'); //used to ignore or clear characters from the input buffer
}