C Exercises: Convert a given roman number to an integer

Last update on August 09 2025 12:47:49 (UTC/GMT +8 hours)

7. Roman Numeral to Integer Variants

Write a C program to convert a Roman number to an integer.

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.
Symbol       Value
I             1
V             5
X             10
L             50
C             100
D             500
M             1000

C Code:

#include <stdio.h>
#include <stdlib.h>
static int roman_to_integer(char c)
{
    switch(c) {
    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;
    }
}

int roman_to_int (char *s)
{
    int i, int_num = roman_to_integer(s[0]);

    for (i = 1; s[i] != '\0'; i++) {
        int prev_num = roman_to_integer(s[i - 1]);
        int cur_num = roman_to_integer(s[i]);
        if (prev_num < cur_num) {
            int_num = int_num - prev_num + (cur_num - prev_num);
        } else {
            int_num += cur_num;
        }
    }
    return int_num;
}
int main(void)
 {
  char *str1 = "XIV";
    printf("Original Roman number: %s", str1);
    printf("\nRoman to integer: %d", roman_to_int(str1));
    return 0;
}

Sample Output:

Original Roman number: XIV
Roman to integer: 14

Pictorial Presentation:

C Programming: Convert a given roman number to an integer.

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to convert a Roman numeral string to an integer, handling subtractive cases correctly.
Write a C program to convert multiple Roman numeral strings to integers and store the results in an array.
Write a C program to implement a case-insensitive Roman numeral to integer conversion.
Write a C program to validate the input Roman numeral and return an error for invalid sequences.

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