CS1101C Lab 2 (Even Week)

Roman Numerals Again

The name of your C program file must be called arabic.c, files with any other name will not be marked.

Preliminary

Roman numerals are used frequently to indicate dates, in particular the year (for example, MMVI represents the year 2006). There are two main differences between roman and arabic numerals.

• There is no symbol for zero in roman numerals;
• Numeral placement in the roman system can indicate either addition or subtraction.

Your task for this lab assignment is to convert a roman numeral to its arabic equivalent. To assist you with character input, a sample code readchar.c is provided below that requests from the user a roman numeral (in fact it can be anything you type) and prints out the characters one at a time. It is up to you whether you wish to use the code; it is optional.

#include <stdio.h>

int main(void)
{
     char ch;

     printf("Enter roman numerals: ");
     do
     {
         scanf("%c", &ch);

         if (ch != '\n')
         {
             printf("Printing one character at a time: %c\n", ch);
         }
     } while (ch != '\n');

     return 0;
}

A sample output is shown below.

$ gcc -Wall readchar.c -o readchar
$ readchar
Enter roman numerals: MMVI
Printing one character : M
Printing one character : M
Printing one character : V
Printing one character : I
$

Notice that we perform explicit checks for the newline character. Why do you think this is needed?

Roman Numeral Conversion

The conversion is specified using the following cases.

• I represents 1. Joining two I's together (i.e. II) represents 2, while III represents 3. However, IIII to represent 4 is forbidden because there is a shorter notation.
• V represents 5. Placing I before V (i.e. IV) will mean subtract I from V, i.e. 4. Note that we do not subtract more than one I from V, so IIV to represent 3 is invalid. Placing I after V (i.e. VI) will mean add I to V, i.e. 6. Likewise, VII and VIII represents 7 and 8. To represent 9 and 10, we do not use VIIII and VV respectively because there exist shorter notations.
• X represents 10. Following the rule above, IX is 9 while XI is 11.
• L represents 50 and works in much the same way as V. So XL is 40 while LX is 60. Additionally, XLI is 41, XLV is 45, XLIV is 44, XLVI is 46, XLIX is 49. Hopefully you get the picture...
• C represents 100.
• D represents 500.
• M represents 1000. M is the last character of the roman numeral system so to represent 9000, there is no choice but to use MMMMMMMMM.

The Task

Write a program arabic.c that requests a roman numeral from the user. The input can either be lowercase, uppercase, or a mix of both. A sample run of the program is shown below. User input is denoted in bold.

$ gcc -Wall arabic.c -o arabic
$ arabic
Enter roman numerals : i
The year in arabic is 1.

$ arabic
Enter roman numerals : MMVI
The year in arabic is 2006.

$ arabic
Enter roman numerals : McMxCvIiI
The year in arabic is 1998.

$ arabic
Enter roman numerals : MMMMMMMMMCMXCIX
The year in arabic is 9999.

$ arabic
Enter roman numerals : mmmmmmmmmdccclxxxviii
The year in arabic is 9888.

$

Points to Note

• For simplicity, we assume that user input is a valid roman numeral which would convert to a number between 1 and 9999. There is no need to perform any explicit checks on the data entered by the user.
• Use only whatever has been covered up till and including Lecture 5. Do not venture beyond that.

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