This post contains a total of 10+ Hand-Picked C Roman to Decimal Converter examples with source code. All the Roman to Decimal converters are made using C Programming Language.
You can use the source code of these programs for educational use with credits to the original owner.
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1. By Noor ❤
Made by Noor ❤. Simple program to convert roman number to decimal. Input : LXX Output : 70, please enter roman no in capital. ( Source )
#include <stdio.h>
#include<string.h>
int convert(char);
int main() {
int i=0, num=0 ;
char r[100];
printf("enter roman number");
scanf("%s",r);
while(r[i])
{
if(convert(r[i])<0) //checking valadity
{
printf("\n Invalid Roman number");
return 0;
}
if((strlen(r)-i)>2)
{
if(convert(r[i])<convert(r[i+2]))//checking valadity
{
printf("\nInvalid Roman number ");
return 0;
}
}
//conversion of roman no into decimal
if(convert(r[i])>=convert(r[i+1]))
num = num + convert(r[i]);
else
{
num = num + (convert(r[i+1])-convert(r[i]));
i++;
}
i++;
}
printf("\n Equivalent decimal number : %d",num);
return 0;
}
int convert(char ch)
{
int i=0;
switch(ch)
{
case 'I':i=1;break;
case 'V':i=5; break;
case 'X':i=10;break;
case 'L':i=50; break;
case 'C':i=100;break;
case 'D':i=500; break;
case 'M':i=1000;break;
case '\0':i=0; break;
default:i=-1;
}
return i;
}2. By Pringle
Made by Pringle. ( Source )
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int main()
{
int a[100],len,i,j,k;
char rom[100];
printf("Enter the Roman Numeral:\n");
scanf("%s",rom);
len=strlen(rom);
for(i=0; i<len; i++)
{
if(rom[i]=='I') a[i]=1;
else if(rom[i]=='V') a[i]=5;
else if(rom[i]=='X') a[i]=10;
else if(rom[i]=='L') a[i]=50;
else if(rom[i]=='C') a[i]=100;
else if(rom[i]=='D') a[i]=500;
else if(rom[i]=='M') a[i]=1000;
else
{
printf("\nInvalid Value");
exit(0);
}
}
k=a[len-1];
for(i=len-1; i>0; i--)
{
if(a[i]>a[i-1]) k=k-a[i-1];
else if(a[i]==a[i-1] || a[i]<a[i-1]) k=k+a[i-1];
}
printf("Its Decimal Equivalent is:");
printf("%d\n",k);
return 0;
}
3. By Win Htay 🇲🇲
Made by Win Htay 🇲🇲. Roman to Decimal Converter, Test by giving Roman Number, You can use lower or upper letter. ( Source )
#include<stdio.h>
#include<string.h>
int GetValue(char c)
{
if(c=='i' || c=='I') return 1;
else if(c=='v' || c=='V') return 5;
else if(c=='x' || c=='X') return 10;
else if(c=='l' || c=='L') return 50;
else if(c=='c' || c=='C') return 100;
else if(c=='d' || c=='D') return 500;
else if(c=='m' || c=='M') return 1000;
return 0;
}
int Roman2Dec(char st[])
{
int n=0;
for(int i=0; i<strlen(st); i++)
{
if(i==strlen(st)-1)
{
n+= GetValue(st[i]); break;
}
int n1 = GetValue(st[i]);
int n2 = GetValue(st[i+1]);
if(n1 >= n2)
n += n1;
else
{
n += n2 - n1;
i++;
}
}
return n;
}
int main()
{
char st[30];
printf("Enter Roman Number : ");
scanf("%s", st);
int n = Roman2Dec(st);
printf("%d", n);
return 0;
}4. By JothiRam
Made by JothiRam. ( Source )
main()
{
char rom[30];
int a[30], l, i, k, dec;
printf("Enter the roman number\n");
scanf("%s", &rom);
l =strlen(rom);
for(i = 0; i < l; i++)
{
switch (rom[i])
{
case 'I': a[i] = 1;
break;
case 'V': a[i] = 5;
break;
case 'X': a[i] = 10;
break;
case 'L': a[i] = 50;
break;
case 'C': a[i] = 100;
break;
case 'D': dec = dec + 500;
break;
case 'M': a[i] = 1000;
break;
default : printf("Invalid choice");
break;
}
}
k = a[l - 1];
for(i = l - 1; i > 0; i--)
{
if(a[i] > a[i - 1])
{
k = k - a[i - 1];
}
if(a[i] <= a[i - 1])
{
k = k + a[i - 1];
}
}
printf("decimal equivalent is %d", k);
}5. By P S V L S SOWJANYA
Made by P S V L S SOWJANYA. ( Source )
#include<stdio.h>
#include<string.h>
int digit(char);
int main(){
char roman_Number[1000];
int i=0;
long int number =0;
scanf("%s",roman_Number);
while(roman_Number[i]){
if(digit(roman_Number[i]) < 0){
printf("Invalid roman digit : %c",roman_Number[i]);
return 0;
}
if((strlen(roman_Number) -i) > 2){
if(digit(roman_Number[i]) < digit(roman_Number[i+2])){
printf("Invalid roman number");
return 0;
}
}
if(digit(roman_Number[i]) >= digit(roman_Number[i+1]))
number = number + digit(roman_Number[i]);
else{
number = number + (digit(roman_Number[i+1]) - digit(roman_Number[i]));
i++;
}
i++;
}
printf("%ld",number);
return 0;
}
int digit(char c){
int value=0;
switch(c){
case 'I': value = 1; break;
case 'V': value = 5; break;
case 'X': value = 10; break;
case 'L': value = 50; break;
case 'C': value = 100; break;
case 'D': value = 500; break;
case 'M': value = 1000; break;
case '\0': value = 0; break;
default: value = -1;
}
return value;
}6. By Abhishek
Made by Abhishek. ( Source )
#include <stdio.h>
#include<string.h>
int main(){
char s1[4000];
long int res=0, n;
int i;
scanf("%s",s1);
n=strlen(s1);
for(i=0;i<n;i++){
if(s1[i]=='I'){
res+=1;
}
else if(s1[i]=='V'){
res+=5;
if(s1[i-1]=='I')
res-=2;
}
else if(s1[i]=='X'){
res+=10;
if(s1[i-1]=='I')
res-=2;
else if(s1[i-1]=='V')
res-=10;
}
else if(s1[i]=='L'){
res+=50;
if(s1[i-1]=='I')
res-=2;
else if(s1[i-1]=='V')
res-=10;
else if(s1[i-1]=='X')
res-=20;
}
else if(s1[i]=='C'){
res+=100;
if(s1[i-1]=='I')
res-=2;
else if(s1[i-1]=='V')
res-=10;
else if(s1[i-1]=='X')
res-=20;
else if(s1[i-1]=='L')
res-=100;
}
else if(s1[i]=='D'){
res+=500;
if(s1[i-1]=='I')
res-=2;
else if(s1[i-1]=='V')
res-=10;
else if(s1[i-1]=='X')
res-=20;
else if(s1[i-1]=='L')
res-=100;
else if(s1[i-1]=='C')
res-=200;
}
else if(s1[i]=='M'){
res+=1000;
if(s1[i-1]=='I')
res-=2;
else if(s1[i-1]=='V')
res-=10;
else if(s1[i-1]=='X')
res-=20;
else if(s1[i-1]=='L')
res-=100;
else if(s1[i-1]=='C')
res-=200;
else if(s1[i-1]=='D')
res-=1000;
}
}
printf("%ld",res);
}7. By Jamerock
Made by Jamerock. ( Source )
#include<stdio.h>
#include<string.h>
//Numerical string to number
int val(char r) {
//Roman Numeral input
if (r == 'I')
return 1;
if (r == 'V')
return 5;
if (r == 'X')
return 10;
if (r == 'L')
return 50;
if (r == 'C')
return 100;
if (r == 'D')
return 500;
if (r == 'M')
return 1000;
return -1;
}
//Roman Number To Decimal
int romannumToDecimal(char arr[]) {
int res = 0;
int i,len=strlen(arr);
for (i=0; i<len; i++) {
int s1 = val(arr[i]);
if (i+1 < len) {
int s2 = val(arr[i+1]);
if (s1 >= s2)
res = res + s1;
else
{
res = res + s2 - s1;
i++;
}
}
//repeat
else
{
res = res + s1;
i++;
}
}
return res;
}
//sub value
int subVal(char num1, char num2, int i, char *c) {
c[i++] = num1;
c[i++] = num2;
return i;
}
//
int value(char ch, int n, int i, char *c) {
int j;
for (j = 0; j < n; j++)
c[i++] = ch;
return i;
}
// Print Roman Numerals
void printRoman(int num) {
char c[10001];
int i = 0;
while (num != 0) {
if (num >= 1000) {
i = value('M', num/1000, i, c);
num = num%1000;
}
else if (num >= 500)
{
if (num < 900) {
i = value('D', num/500, i, c);
num = num%500;
}
else
{
i = subVal('C', 'M', i, c);
num = num%100 ;
}
}
else if (num >= 100) {
if (num < 400) {
i = value('C', num/100, i, c);
num = num%100;
}
else {
i = subVal('C','D',i,c);
num = num%100;
}
}
else if (num >= 50 ) {
if (num < 90) {
i = value('L', num/50,i,c);
num = num%50;
}
else {
i = subVal('X','C',i,c);
num = num%10;
}
}
else if (num >= 10)
{
if (num < 40) {
i = value('X', num/10,i,c);
num = num%10;
}
else
{
i = subVal('X','L',i,c);
num = num%10;
}
}
else if (num >= 5)
{
if (num < 9) {
i = value('V', num/5,i,c);
num = num%5;
}
else {
i = subVal('I','X',i,c);
num = 0;
}
}
else if (num >= 1) {
if (num < 4) {
i = value('I', num,i,c);
num = 0;
}
else {
i = subVal('I', 'V', i, c);
num = 0;
}
}
}
//
int j;
for (j = 0; j < i; j++)
printf("%c", c[j]);
}
//
int main() {
char arr1[100];
char arr2[100];
scanf("%s %s",arr1,arr2);
int val1=romannumToDecimal(arr1);
int val2=romannumToDecimal(arr2);
printRoman(val1+val2);
//Call input file and ouput file
FILE *ifp, *ofp;
char *mode = "w";
char outputFilename[] = "ROMAN.TXT";
ifp = fopen("ROMAN.TXT", mode);
if (ifp == NULL) {
fprintf(stderr, "Can't open input file ROMAN.TXT!\n");
exit(1);
}
ofp = fopen(outputFilename, "w");
if (ofp == NULL) {
fprintf(stderr, "Can't open output file %s!\n",
outputFilename);
exit(1);
}
fclose(ifp);
fclose(ofp);
return 0;
}8. By Caleb Brown
Made by CB93. An application written in C that converts roman numeral values into their equivalent decimal values. ( Source )
// Roman_Decimal.c
// Date: June 27, 2018
#define _CRT_SECURE_NO_WARNINGS
#define SIZE 10
#include < stdio.h >
#include < ctype.h >
convertRoman(int * decimalNum, int * previousNum, int * bool);
checkPrevious(const int amount, int ** val, const int previousNum);
// Runs the Program
int main(void)
{
int num = 0, decimalNum = 0, previousNum = 0, count, bool = 1, getch(void);
printf("10 Roman numeral values will be input and converted into\n"
"their equivalent Hindu - Arabic numeric values.\n");
for (count = 0; count < SIZE; count++)
{
printf("\nInput Roman numeral #: %d ", count + 1);
convertRoman(&decimalNum, &previousNum, &bool);
(bool ? printf(" = %d\n", decimalNum) : printf(
"Error - last character was not valid!!!\n")); // If TRUE
decimalNum = 0, num = 0, previousNum = 0;
bool = 1; // TRUE
}
printf("THATS ALL FOLKS :)");
getch();
}
// Takes in roman numeral chars and converts into numeric values
convertRoman(int * decimalNum, int * previousNum, int * bool)
{
int M = 1000, D = 500, C = 100, L = 50, X = 10, V = 5, I = 1;
char input;
while (((input) = getchar()) != '\n')
{
switch (toupper(input))
{
case 'I':
*decimalNum += I; // Increment by 1
checkPrevious(I, &decimalNum, *previousNum); *previousNum = I;
break;
case 'V':
*decimalNum += V; // Increment by 5
checkPrevious(V, &decimalNum, *previousNum); *previousNum = V;
break;
case 'X':
*decimalNum += X; // Increment by 10
checkPrevious(X, &decimalNum, *previousNum); *previousNum = X;
break;
case 'L':
*decimalNum += L; // Increment by 50
checkPrevious(L, &decimalNum, *previousNum); *previousNum = L;
break;
case 'C':
*decimalNum += C; // Increment by 100
checkPrevious(C, &decimalNum, *previousNum); *previousNum = C;
break;
case 'D':
*decimalNum += D; // Increment by 500
checkPrevious(D, &decimalNum, *previousNum); *previousNum = D;
break;
case 'M':
*decimalNum += M; // Increment by 1000
checkPrevious(M, &decimalNum, *previousNum); *previousNum = M;
break;
default:
* bool = 0; // FALSE
break;
}
}
}
// Detects when to apply subtractive notation from passed previousChar and currentChar
checkPrevious(const int currentChar, int ** val, const int previousChar)
{
if (previousChar < currentChar)
{
** val -= (2 * previousChar);
}
}9. By Ramongr
Made by Ramongr. Transforms roman numerals to decimal value. ( Source )
/*
####################################################################
GLOBAL INCLUDES
####################################################################
*/
#include <stdio.h>
#include <string.h>
/*
####################################################################
CODE
####################################################################
*/
//This function assumes the string is in the correct roman form and in CAPS
int
roman_to_dec(char *roman){
int i,sum;
char letter='I';
i=0;
while(roman[i++])
sum = 0;
while(i>=0){
switch(roman[i]){
case 'I':
if(letter == 'V'){
sum -=1;
}else{
sum +=1;
}
break;
case 'V':
if(letter == 'X'){
sum -=5;
}else{
sum +=5;
letter = 'V';
}
break;
case 'X':
if(letter == 'L'){
sum -=10;
}else{
sum +=10;
letter = 'X';
}
break;
case 'L':
if(letter == 'C' || letter == 'D'){
sum -=50;
}else{
sum +=50;
letter = 'L';
}
break;
case 'C':
if(letter == 'D' || letter == 'M'){
sum -=100;
}else{
sum +=100;
letter = 'C';
}
break;
case 'D':
if(letter == 'M'){
sum -=500;
}else{
sum +=500;
letter = 'D';
}
break;
//There are bigger numbers, but are not supported by ASCII
case 'M':
sum +=1000;
letter = 'M';
break;
}
i--;
}
printf("%d\n", sum);
}
int
main(int argc, char **argv){
roman_to_dec(argv[1]);
return 0;
}10. By Harjas Dot
Made by Harjas Dot. A ‘C’ program to convert Roman numerals to Decimal expression and vice versa. ( Source )
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char arr[],val[10];
int a,x=0,l,c=0,b,d,e=0,f=0,g,h=1;
int test(),result(),vidx();
int main()
{
while(h!=0)
{
printf("\nIF YOU WANT TO CONVERT DECIMAL TO ROMAN PRESS 1\n");
printf("IF YOU WANT TO CONVERT ROMAN TO DECIMAL PRESS 2\n");
printf("IF YOU WNT TO EXIT PRESS 3\n");
scanf("%d",&b);
if(b==1 || b==2)
{
vidx();
}
else
{
h=0;
}
}
printf("THANK YOU!!!!");
return 0;
}
//---------------
vidx()
{
if(b==1){
printf("YOUR NUMBER MUST BE LESS THAN 4000 \n");
printf("Enter the decimal number: ");
scanf("%d",&a);
while (a!=0)
{
test();
//printf("%d",a);
}
//printf("%d",c);
result();
memset(arr,0,c);
}
else
{
printf("ENTER THE ROMAN EXPRESSION IN CAPITAL\n");
scanf("%s",val);
for(d=0;d<10;d+=1)
{
f=val[d];
if(f=='I')
{
d+=1;
g=val[d];
if(g=='I'){
e+=2;
}
else if(g=='V'){
e+=4;
}
else if(g=='X'){
e+=9;
}
else
{
e+=1;
d-=1;
}
}
//-----------------------------------------------------------------------
else if(f=='V')
{
e+=5;
}
else if(f=='X')
{
d+=1;
g=val[d];
if(g=='L')
{
e+=40;
}
else if(g=='C'){
e+=90;
}
else
{
e+=10;
d-=1;
}
}
else if(f=='L')
{
e+=50;
}
else if(f=='C')
{
d+=1;
g=val[d];
if(g=='D'){
e+=400;
}
else if(g=='M'){
e+=900;
}
else{
e+=100;
d-=1;
}
}
else if(f=='D'){
e+=500;
}
else if(f=='M'){
e+=1000;
}
}
}
printf("\n%d",e);
memset(val,0,10);
e=0;
}
//-------------------
test()
{
if(a>=1 && a<5)
{
if(a==4)
{
arr[x]='i';
c+=1;
x+=1;
arr[x]='v';
c+=1;
x+=1;
a-=4;
}
else
{
arr[x]='i';
c+=1;
x+=1;
a-=1;
}
}
else if(a>=5 && a<10)
{
if(a==9)
{
arr[x]='I';
c+=1;
x+=1;
arr[x]='X';
c+=1;
x+=1;
a-=9;
}
else
{
arr[x]='V';
c+=1;
x+=1;
a-=5;
}
}
else if(a>=10 && a<50)
{
if(a>=40){
arr[x]='X';
c+=1;
x+=1;
arr[x]='L';
c+=1;
x+=1;
a-=40;
}
else{
arr[x]='X';
c+=1;
x+=1;
a-=10;
}
}
else if(a>=50 && a<100){
if(a>=90){
arr[x]='X';
c+=1;
x+=1;
arr[x]='C';
c+=1;
x+=1;
a-=90;
}
else{
arr[x]='L';
x+=1;
c+=1;
a-=50;
}
}
else if(a>=100 && a<500){
if(a>=400){
arr[x]='C';
x+=1;
c+=1;
arr[x]='D';
x+=1;
c+=1;
a-=400;
}
else{
arr[x]='C';
c+=1;
x+=1;
a-=100;
}
}
else if(a>=500 && a<1000){
if(a>=900){
arr[x]='C';
c+=1;
x+=1;
arr[x]='M';
c+=1;
x+=1;
a-=900;
}
else{
arr[x]='D';
x+=1;
c+=1;
a-=500;
}
}
else if(a>=1000 && a<4000){
arr[x]='M';
c+=1;
x+=1;
a-=1000;
}
else{
printf("U ENTERED A NUMBER WHICH IS MORE THAN OR EQUAL TO 4000 ");
a-=a;
}
}
result()
{
for(l=0;l<c;l=l+1)
{
printf("%c",arr[l]);
}
}11. By PRASADsiva
Made by PRASADsiva. ( Source )
#include<stdio.h>
#include<string.h>
int d(char);
int main(){
char rN[1000];
int i=0;
long int n =0;
scanf("%s",rN);
while(rN[i]){
if(d(rN[i]) < 0){
printf("Invalid roman digit : %c",rN[i]);
return 0;
}
if((strlen(rN) -i) > 2){
if(d(rN[i]) < d(rN[i+2])){
printf("Invalid roman number");
return 0;
}
}
if(d(rN[i]) >= d(rN[i+1]))
n = n + d(rN[i]);
else{
n = n + (d(rN[i+1]) - d(rN[i]));
i++;
}
i++;
}
printf("%ld",n);
return 0;
}
int d(char c){
int value=0;
switch(c){
case 'I': value = 1; break;
case 'V': value = 5; break;
case 'X': value = 10; break;
case 'L': value = 50; break;
case 'C': value = 100; break;
case 'D': value = 500; break;
case 'M': value = 1000; break;
case '\0': value = 0; break;
default: value = -1;
}
return value;
}