by This is a very standard which is being asked in many interview questions. Here we are going to write the program in C which will convert Roman numbers into decimal number up to 3999 values. Before going ahead let’s revise what each roman literals means:
M = 1000
D = 500
C = 100
L = 50
X = 10
V = 5
I = 1
Here is C program to solve the above problem.
#include <unistd.h>
#include <stdio.h>
#include <stdbool.h>
#define ROMAN_NUMBER_LENGTH 20
int romanToDecimal (char *ch)
{
switch (*ch)
{
case 'I':
return 1;
case 'V':
return 5;
case 'X':
return 10;
case 'L':
return 50;
case 'C':
return 100;
case 'D':
return 500;
case 'M':
return 1000;
default:
return 0;
}
}
/* We need to check next char for 'I', 'X' and 'C' character as
* these characters can come before some other characters which
* have different values than usual */
int checkNextChar (char *ch, int *index)
{
bool incrIndex = true;
int val = 0;
switch (ch[*index])
{
case 'I':
if (ch [*index + 1] == 'V')
{
val = 4;
}
else if (ch [*index + 1] == 'X')
{
val = 9;
}
else
{
incrIndex = false;
val = 1;
}
break;
case 'X':
if (ch [*index + 1] == 'L')
{
val = 40;
}
else if (ch [*index + 1] == 'C')
{
val = 90;
}
else
{
incrIndex = false;
val = 10;
}
break;
case 'C':
if (ch [*index + 1] == 'D')
{
val = 400;
}
else if (ch [*index + 1] == 'M')
{
val = 900;
}
else
{
incrIndex = false;
return 100;
}
break;
default:
incrIndex = false;
return romanToDecimal (&ch[*index]);
}
if (incrIndex)
{
*index = *index + 1;
}
return val;
}
int converter (char *roman)
{
int total = 0;
for (int i = 0; i < ROMAN_NUMBER_LENGTH ; i++)
{
if (roman[i] == '\0')
{
break;
}
total = total + checkNextChar (roman, &i);
}
return total;
}
int main ()
{
char roman[ROMAN_NUMBER_LENGTH] = "";
printf ("Enter Roman number: \n");
scanf ("%s", roman);
printf ("Entered Number is : %s \n", roman);
printf ("Equivalent Number is: %d \n", converter (roman));
}
Output of above program is as follows:
Enter Roman number:
MCDXLIV
Entered Number is : MCDXLIV
Equivalent Number is: 1444
Enter Roman number:
MCDLXVIII
Entered Number is : MCDLXVIII
Equivalent Number is: 1468
