Roman Numeral.cpp

#include <stdio.h>
#include <windows.h>
  
#define MAX_ARRAY_SIZE 7
#define BAD_NUMERAL   -1
  
void ConvertRToD();
int  GetVal( char Letter, char RomanNum[], int DecNum[] );
  
int main ( ) {
    int UserChoice = -1;
      
    printf("Welcome to Taylor's and Korben's Roman Numeral Calc\n\n");
      
    while( UserChoice != 0 ) {
             
        printf("0. Exit\n1. Convert Roman Numeral -> Decimal\n\nChoice: ");
          
        scanf("%d", &UserChoice);
          
        switch( UserChoice )  {
      
            case 0:
              break;
            case 1:
              ConvertRToD();
            break;
            default:
              printf("\nInvalid choice (%d)\n\n", UserChoice);
            break;
              
        }
    } 
      
    printf("\n");
      
    system("pause");
}
  
void ConvertRToD(){
       
      // Flush old input buffer, or fgets will be skipped, do to \n's left in the buffer. 
      // fflush may not work on all compilers
      fflush(stdin);
       
      // We will use parrell arrays, not switch :)
      int  DecimalNum[MAX_ARRAY_SIZE] = { 1,   5,  10,  50,  100, 500, 1000 };
      char RomanNums [MAX_ARRAY_SIZE] = { 'I','V', 'X', 'L', 'C', 'D', 'M'  };
  
      // Vars we will use
      int DecimalValue = 0, RomanLen = 0;
        
      // Make the array large enough for even the biggest of RN's
      char RomanValue[ 15 ];
        
      printf("\nPlease enter a roman numeral: ");
        
      // Get the input
      fgets( RomanValue, sizeof( RomanValue ), stdin );
        
      // Get the size of the used array (that has our string in it)
      RomanLen = strlen(RomanValue) - 1;
        
      // We want to make sure there is a null term char where our string ends. 
      // A lack of one would cause unwanted results
      RomanValue[RomanLen] = '\0';
  
      // Begin loop
      int i = 0;
      for(i; i < RomanLen; i++)
      {  
         // Read chars
         char CurrChar = RomanValue[i];
         char NextChar = RomanValue[i + 1];
           
         // Read Vals
         int  CurrVal  = GetVal( CurrChar, RomanNums, DecimalNum );
         int  NextVal  = GetVal( NextChar, RomanNums, DecimalNum );
           
         if( ( CurrVal == BAD_NUMERAL && CurrChar != '\0' ) || ( NextVal == BAD_NUMERAL && NextChar != '\0' ) )
         {
             printf("\nInvalid roman numeral, returning to main menu...\n\n");
             return; // Get out of this func, go back to the loop
         }
           
         if( NextVal > CurrVal )
             DecimalValue -=  CurrVal;  
         else
             DecimalValue +=  CurrVal;  
      }
         
    printf("\n%s in decimal is %d\n\n", RomanValue, DecimalValue); 
}
  
int GetVal( char Letter, char RomanNum[], int DecNum[] ) {
       int i = 0;
         
       for(i; i < MAX_ARRAY_SIZE; i++ ) {
                
            if( Letter == RomanNum[i] )
                return DecNum[i];
       }
         
       return BAD_NUMERAL;
}