Roman no.system to Decimal no. system converting

Can anyone give me somewhere to start if
I have to convert from Roman Numeral to decimals?

M - 1000
D - 500
C - 100
L - 50
X - 10
V - 5
I - 1

that if the user inputs CD - 400
MD - 1500
IX - 9
MXIII - 1013

I just need a rough guide on how to do this.
All I know is if the digit's value before is smaller, then subtracts and if not, just keep adding. any example would help me greatly. thanks.

PS: how do I also make the scanf determine the number of letters input?

 

This might work. It isn't complete by any means, but is a general approach.

Code:

Code:

char numerals[80];
int numeralCount,i;
int firstValue,secondValue;
scanf("%s",numerals);
printf("You entered: %s\n",numerals);
numeralCount = strlen(numerals);
for (i = 0; i < numeralCount; i++) {
	printf("%c\n",numerals[i]);
	if (i != (numeralCount - 1)) {   // not on last character
		firstValue = getValue(numerals[i]);    // return 1000 for 'M', etc....
		secondValue = getValue(numerals[i+1]);
		if (firstValue < secondValue) {
			// do your 'less than' magic
			i++;   // 'consume' the second char, since you want to step over it next time
		}
		else {
			// just add the value
		}
	}
	else {   // on last character
		// to get here, must need to add final char value
	}
}

note that when you have a 'less than' case, like IV, you want the next time thru the loop to skip to the character after the V. That's what the i++ 'consume' is for.

You'd have a 'finalValue' variable or some such that got added to each time thru the loop, and at the end would be your final result.

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Beginner Computer Programming
teaching programming to beginners using C

 

Use strlen on the string, or some loop like this:
Code:

Code:

char ch;
while (scanf("%c",&ch)) {
      [ verfify ch ]
      [ add value to total ] // see note below
}

Or scanf's %n modifier, like this:
Code:

Code:

#include <stdio.h>

int main()
{
  char buf[1024];
  int bufLength;
  if(scanf("%1023s%n", buf, &bufLength)) {
    printf("Your string has a length of %d\n", bufLength);
  }
}