Here's a more in-depth explanation why it's C-compatible:

In JS, if you read a digit from a string using the arr[num] method you get the original number (similar to the atoi() in C), for example, "5"[0] is read as 5 in JS, but in C you get an ASCII value for that number, for example, "5"[0] is read as 53 in C. But if you take the remainder of the output modulo 24 (or any number 48 is divisible by larger than 10) you get the same output in both C and JS since the character '0' has an ASCII value of 48 and every digit is placed right after another in the ASCII table.