Javascript Practice 78: JS Hero - Roman numerals II

 

Question: 

Write a function roman that converts an Arabic number (up to 1000) into a Roman numeral.

Example: roman(483) should return 'CDLXXXIII'.

Answer: 

function roman (n) {

let romanObj = {

M: 1000, 

CM: 900, 

D: 500,

CD: 400,

C: 100,

XC: 90,

L: 50,

XL: 40,

X: 10,

IX: 9,

V: 5,

IV: 4,

I: 1

};

let roman2 = ''; 

for (let key in romanObj) {

while (n >= romanObj[key]) {

roman2 += key;

n -= romanObj[key]; 

}

}

return roman2; 

}; 

> we declare a function 'roman'

> it has one parameter 'n'

> we declare a variable ‘romanObj’ 

> we initialize it with roman numerals and their values in ‘key: value’ format

> like this: {I:1, V:5, X:10, etc}

> thus we make the variable ‘romanObj’ an object; that holds multiple values in terms of properties and methods

> we declare another variable ‘roman2’ and it is an empty string

> we leave it empty as we shall initialize it later by adding the roman version of the integers and then return it later

> we first use the ‘for in loop’ to loop through every key value pair of the ‘romanObj’ object

> to access the key; we can log the key or console.log(‘key: ‘, key) / console.log(key)

> to access the value; we can log the value or console.log(‘value: ‘, romanObj[key]) / console.log(romanObj[key])

> inside this ‘for in loop’ we run another ‘while loop’ 

> so while our number ‘n’ is greater than or equal to the value or romanObj[key], then in that case we want to add the value to roman2; our value will be the key

> like this: roman2 += key

> every time a key is added to the ‘roman2’ variable we also need to subtract that key value from our number ‘n’

> like this: n -= romanObj[key]

> so the while loop iteration keeps looping till our number ‘n’ is less than romanObj[key] or the key value

> the while loop stops when ‘n’ is less than romanObj[key] or the key value

> after that the outer ‘for in loop’ stops 

> and then we can return roman2