Roman to Integer Conversion in DSA C - Build from Scratch

Roman to Integer Conversion

📖 Scenario: You are building a simple tool to convert Roman numerals into regular numbers. Roman numerals are used in clocks, books, and old movies. Your program will help translate these symbols into numbers we use every day.

🎯 Goal: Build a program that takes a Roman numeral string and converts it into its integer value using basic C programming concepts.

📋 What You'll Learn

Create a function to map Roman numeral characters to their integer values

Use a loop to process each character in the Roman numeral string

Handle the subtraction rule where a smaller numeral before a larger numeral means subtraction

Print the final integer result

💡 Why This Matters

🌍 Real World

Roman numerals are used in clocks, book chapters, movie titles, and historical documents. Converting them to integers helps in calculations and comparisons.

💼 Career

Understanding string processing, conditional logic, and loops in C is fundamental for software development, embedded systems, and working with legacy data formats.

1

Create the Roman numeral string

Create a character array called roman and initialize it with the string "MCMXCIV" which represents the Roman numeral for 1994.

DSA C

char roman[] = "MCMXCIV";  // Your code here

Hint

Use double quotes to create a string in C, and assign it to a character array.

2

Create a function to get integer value of Roman characters

Write a function called value that takes a char parameter r and returns the integer value of the Roman numeral character. Use switch to return 1000 for 'M', 500 for 'D', 100 for 'C', 50 for 'L', 10 for 'X', 5 for 'V', and 1 for 'I'. Return 0 for any other character.

DSA C

char roman[] = "MCMXCIV";

int value(char r) {
    // Your code here
}

Hint

Use a switch statement to return the correct integer for each Roman numeral character.

3

Convert the Roman numeral to integer

Write a function called romanToInt that takes the character array roman and returns the integer value. Use a for loop to iterate through the string. For each character, compare its value with the next character's value. If the current value is less than the next, subtract it from the result; otherwise, add it. Use the value function to get integer values.

DSA C

char roman[] = "MCMXCIV";

int value(char r) {
    switch(r) {
        case 'M': return 1000;
        case 'D': return 500;
        case 'C': return 100;
        case 'L': return 50;
        case 'X': return 10;
        case 'V': return 5;
        case 'I': return 1;
        default: return 0;
    }
}

int romanToInt(char* roman) {
    // Your code here
}

Hint

Use a while loop to check each character and compare with the next. Add or subtract accordingly.

4

Print the converted integer

In the main function, call romanToInt with the roman string and print the returned integer using printf.

DSA C

char roman[] = "MCMXCIV";

int value(char r) {
    switch(r) {
        case 'M': return 1000;
        case 'D': return 500;
        case 'C': return 100;
        case 'L': return 50;
        case 'X': return 10;
        case 'V': return 5;
        case 'I': return 1;
        default: return 0;
    }
}

int romanToInt(char* roman) {
    int result = 0;
    int i = 0;
    while (roman[i]) {
        int s1 = value(roman[i]);
        int s2 = value(roman[i + 1]);
        if (s1 < s2) {
            result += s2 - s1;
            i += 2;
        } else {
            result += s1;
            i++;
        }
    }
    return result;
}

int main() {
    // Your code here
}

Hint

Call romanToInt with roman and print the result using printf.