Question

I’m writing code that takes a number from a user and prints in back in letters as string. I want to know, which is better performance-wise, to have if statements, like

if (n < 100) {
    // code for 2-digit numbers
} else if (n < 1000) {
    // code for 3-digit numbers
} // etc..

or to put the number in a string and get its length, then work on it as a string.

The code is written in C++.

Answer 1

Of course if-else will be faster.

To compare two numbers you just compare them bitwise (there are different ways to do it but it’s a very fast operation).

To get the length of the string you will need to make the string, put the data into it and compute the length somehow (there can be different ways of doing it too, the simplest being counting all the symbols). Of course it takes much more time.

On a simple example though you will not notice any difference. It often amazes me that people get concerned with such things (no offense). It will not make any difference for you if the code will execute in 0.003 seconds instead of 0.001 seconds really… You should make such low-level optimizations only after you know that this exact place is a bottleneck of your application, and when you are sure that you can increase the performance by a decent amount.