What is the best way to get right most number in an integer with C?

Question

I'm just mucking around with C as a learner, and wrote this little function...

char *getPlaceSuffix(int number) {

    static char *suffixes[] = {"st", "nd", "rd", "th"};

    if (number >= 11 && number <= 13) {
        return suffixes[3];
    } else {
        while (number > 10) {
            number -= 10;   
        }

        if (number >= 1 && number <= 3) {
            return suffixes[number - 1];
        } else {
            return suffixes[3];
        }               
    }
}   

I tweeted the link, and Konrad Rudolph informed me my method of getting the least significant number was O(n) and not very efficient.

Unfortunately, it’s O(n) for very large number – to make it O(logn), adjust the while loop for higher powers of 10 …

Source

I'm not too familiar with Big O notation, but I get the gist that O(n) isn't too efficient?

As you can see from my code sample, I deduct 10 until the number is one digit long, so I can compare it to see which suffix is appropriate. I had a quick play with division and modulus but couldn't figure it out.

So, my question is, what is the best way to get the least significant digit in a number?

I'm still learning, so please go easy on me :)

Thanks!

Answer 1

number % 10

should work.

Answer 2

"had a quick play with division and modulus but couldn't figure it out."

 number = number % 10

will do it

And if we're really bothered about efficiency for this code (why?) then

char *getPlaceSuffix(int number) {

    static char *suffixes[] = {"th", "st", "nd", "rd", "th",  "th", "th", "th", "th", "th"};
    int h = number %100;
    int d = number %10
    return (h == 11 or h == 12 or h == 13)? suffixes[0]:suffixes[d];
} 

Answer 3

Modulus:

number = number % 10;

Answer 4

Can you just take the number and mod it by 10 and that's your least significant number? When you are deducting by 10 until you can't anymore, you're exactly what modulus was meant for.

Answer 5

Another way will be to sprintf to write the number to a buffer, read the last char.