# 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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