javascript--converts a decimal number to a Roman numeral display

Afternoon on the FCC (freecodecamp) Chinese online to do an exercise: the given number into Roman numerals . Tortured for one hours, finally can give the basic ability to achieve. The process is as follows:

About Roman Numerals

A detailed description of the Roman numerals can be found in Baidu, or Roman numerals. Here is a brief introduction (the picture is selected from Roman numerals):

1. Roman numerals use 7 Roman letters (uppercase) as numbers, representing the following decimal numbers:

          

some numbers are represented by Roman numerals:

                 

2. Counting rules for Roman numerals:

(1) The same number ligatures, the value is added, such as III = 3;

(2) The small number on the right side of the large number, is also cumulative, such as VI = 6;

(3) The small number on the left side of the large number, resulting in a large number of decreases, such as IV = 4;

(4) A horizontal line is drawn above the number, indicating an enlargement of 1000 times times.

A simple and rude example:

            

However, we will encounter some special situations:

(1) 3999 = mmmcmxcix,3999 = MMMDCCCCLXXXXVIIII, both of the results are 3999, but we generally choose simple, that is, the former;

(2) Similarly, 3444 = Mmmcdxliv, 3444 = MMMCCCCXXXXIIII, is also the way to choose the former.

So, first put 1~9 the situation to enumerate:

It can be seen that the Roman numerals on the treatment of 4 and 9 are different with others.

List 4, 9 related parts of the figures:

Ideas and code implementation

1. First convert the numbers into corresponding Roman letters, such as 3999 = MMMDCCCCLXXXXVIIII;

2. Replace the 4 and 9 cases by replacing () to make 3999 = Mmmcmxcix.

1 function convert (num) {
 2 var newArr = [];
 3 var newStr;
 4 // Convert numbers to corresponding Roman letters first
 5 while (num> 0) {
 6 if (num-1000> = 0) {
 7 newArr.push (‘M’);
 8 num-= 1000;
 9} else if (num-500> = 0) {
10 newArr.push (‘D’);
11 num-= 500;
12} else if (num-100> = 0) {
13 newArr.push (‘C’);
14 num-= 100;
15} else if (num-50> = 0) {
16 newArr.push (‘L’);
17 num-= 50;
18} else if (num-10> = 0) {
19 newArr.push (‘X’);
20 num-= 10;
21} else if (num-5> = 0) {
22 newArr.push (‘V’);
23 num-= 5;
24} else if (num-1> = 0) {
25 newArr.push (‘I’);
26 num-= 1;
27}
28}
29 newStr = newArr.join (‘‘);
30 // Replace the 4 and 9 cases
31 newStr = newStr.replace (/ VI {4} | LX {4} | DC {4} | I {4} | X {4} | C {4} / g, function (match) {
32 switch (match) {
33 case ‘VIIII’:
34 return "IX";
35 case ‘LXXXX’:
36 return "XC";
37 case ‘DCCCC’:
38 return "CM";
39 case ‘IIII’:
40 return "IV";
41 case ‘XXXX’:
42 return "XL";
43 case ‘CCCC’:
44 return "CD";
45}
46});
47 return newStr;
48} 

Test some numbers:

console.log(convert(3999));    // MMMCMXCIX
console.log(convert(3444));    // MMMCDXLIV
console.log(convert(1234));   // MCCXXXIV 
console.log(convert(83));    // LXXXIII 
console.log(convert(123));   // CXXIII

At this point, the basic functionality has been implemented.

In addition, the first thousands of smaller numbers are tested with a for loop, which can be converted normally, and the larger number will be longer because there is no processing of 5000,10000.

javascript--converts a decimal number to a Roman numeral display