# C program to convert roman numbers to decimal numbers

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Given below is an algorithm to convert roman numbers to decimal numbers in C language −

## Algorithm

Step 1 − Start

Step 2 − Read the roman numeral at runtime

Step 3 − length: = strlen(roman)

Step 4 − for i = 0 to length-1 do

Step 4.1 − switch(roman[i])

Step 4.1.1 − case ‘m’:

Step 4.1.2 − case ‘M’:

Step 4.1.2.1 − d[i]: =1000

Step 4.1.3 − case ‘d’:

Step 4.1.4 − case ‘D’:

Step 4.1.4.1 − d[i]: =500

Step 4.1.5 − case ‘c’:

Step 4.1.6 − case ‘C’:

Step 4.1.6.1 − d[i]: =100

Step 4.1.7 − case ‘l’:

Step 4.1.8 − case ‘L’:

Step 4.1.8.1 − d[i]: =50

Step 4.1.9 − case ‘x’:

Step 4.1.10 − case ‘X’:

Step 4.1.10.1 − d[i]: =10

Step 4.1.11 − case ‘v’:

Step 4.1.12 − case ‘V’:

Step 4.1.12.1 − d[i]: =5

Step 4.1.13 − case ‘i’:

Step 4.1.14 − case ‘I’:

Step 4.1.14.1 − d[i]: =1

Step 5 − for i =0 to length-1 do

Step 5.1 − if (i==length-1) or (d[i]>=d[i+1]) then

Step 5.1.1 − deci += d[i]

Step 5.2 − else

Step 5.2.1 − deci -= d[i]

Step 6 − Print the decimal equivalent of roman numeral

Step 7 − Stop

## Program

Following is the C program to convert roman numbers to decimal numbers

#include <stdio.h>
#include <conio.h>
main(){
char roman[30];
int deci=0;
int length,i,d[30];
printf("The Roman equivalent to decimal");
printf("Decimal:.........Roman");
printf("%5d............%3c",1,'I');
printf("%5d............%3c",5,'V');
printf("%5d............%3c",10,'X');
printf("%5d............%3c",50,'L');
printf("%5d............%3c",100,'C');
printf("%5d............%3c",500,'D');
printf("%5d............%3c",1000,'M');
printf("Enter a Roman numeral:");
scanf("%s",roman);
length=strlen(roman);
for(i=0;i<length;i++){
switch(roman[i]){
case 'm':
case 'M': d[i]=1000; break;
case 'd':
case 'D': d[i]= 500; break;
case 'c':
case 'C': d[i]= 100; break;
case 'l':
case 'L': d[i]= 50; break;
case 'x':
case 'X': d[i]= 10; break;;
case 'v':
case 'V': d[i]= 5; break;
case 'i':
case 'I': d[i]= 1;
}
}
for(i=0;i<length;i++){
if(i==length-1 || d[i]>=d[i+1])
deci += d[i];
else
deci -= d[i];
}
printf("The Decimal equivalent of Roman numeral %s is %d", roman, deci);
}

## Output

When the above program is executed, it produces the following result −

The Roman equivalent to decimal
Decimal:.........Roman
1............ I
5............ V
10............ X
50............ L
100............ C
500............ D
1000............ M
Enter a Roman numeral: M
The Decimal equivalent of Roman Numeral M is 1000
Updated on 01-Sep-2021 09:04:49