User input; quick question.

[fred via Digitalmars-d-learn]

import std.stdio;

I am somewhat new to D, and I am trying to receive user input, 
like this, with a prompt:

string str;
writeln("Enter a string: ");
str = readln;
writeln(str);

However, the prompt appears after I enter the input; any reason 
why?

I've trawled the internet for a good hour, but I can't seem to 
find an answer.