JavaScript: Convert Roman Numeral to Integer

JavaScript Math: Exercise-22 with Solution

Write a JavaScript function that converts Roman numerals to integers.

Sample Solution:

JavaScript Code:

// Define a function named roman_to_Int that converts a Roman numeral to an integer.
function roman_to_Int(str1) {
    // Check if str1 is null, if so, return -1.
    if(str1 == null) return -1;
    // Initialize the variable num with the integer value of the first character in str1.
    var num = char_to_int(str1.charAt(0));
    var pre, curr;

    // Iterate through the characters of str1 starting from the second character.
    for(var i = 1; i < str1.length; i++){
        curr = char_to_int(str1.charAt(i)); // Get the integer value of the current character.
        pre = char_to_int(str1.charAt(i-1)); // Get the integer value of the previous character.
        // If the current character's value is less than or equal to the previous character's value, add it to num.
        if(curr <= pre){
            num += curr;
        } else {
            // If the current character's value is greater than the previous character's value, subtract twice the previous character's value and add the current character's value to num.
            num = num - pre*2 + curr;
        }
    }

    // Return the final integer value of the Roman numeral.
    return num;
}

// Define a function named char_to_int that returns the integer value of a Roman numeral character.
function char_to_int(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 -1; // Return -1 for invalid characters.
    }
}

// Output the integer value of the Roman numeral 'XXVI' to the console.
console.log(roman_to_Int('XXVI'));
// Output the integer value of the Roman numeral 'CI' to the console.
console.log(roman_to_Int('CI'));

Output:

26
101

Visual Presentation:

Flowchart:

Live Demo:

See the Pen javascript-math-exercise-22 by w3resource (@w3resource) on CodePen.

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