I didn't want to necropost, but I ran into the same behaviour as in this post:
https://forum.dlang.org/post/yfybveovbknvvxmioivd@forum.dlang.org
and was just curious to understand it better.

If I call readln() after having previously called readf(), it does not behave as expected:

import std.stdio, std.string;

void main()
{
    write("Please enter a number: ");
    double number;
    readf(" %s", number);

    write("Please enter a string: ");
    string input = strip(readln());

    writefln!("number: %s --- string: %s")(number, input);
}

Gives me the following:

Please enter a number: 1
Please enter a string: number: 1 ---- string:

I know I can get this to work replacing the strin(readln()) with readf(" %s\n", input), but I also found if I just call strip(readln()) an extra time this worked as well, but what is confusing to me is if I have multiple readf's I still only need to call readln one extra time to get it to work as expected:

import std.stdio, std.string;

void main()
{
    write("Please enter a number: ");
    double number1;
    readf(" %s", number1);
    write("Please enter a number: ");
    double number2;
    readf(" %s", number2);

    // Handle what should be two \n's from readf?
    string input = strip(readln());

    // Continue as normal
    write("Please enter a string: ");
    input = strip(readln());

    writefln!("number1: %s --- number2: %s --- string: %s")
        (number1, number2, input);
}

And this works.

Please enter a number: 1
Please enter a number: 2
Please enter a string: hello
number1: 1 --- number2: 2 --- string: hello

Could anyone help explain this to me, and also is there a better way to handle this when wanting to use a mix of readf and readln?

On Saturday, 24 April 2021 at 14:46:06 UTC, PinDPlugga wrote:

https://dlang.org/library/std/string/chomp.html

On Saturday, 24 April 2021 at 22:13:45 UTC, Ali Çehreli wrote:

Hi Ali,

Being a new D learner, I've noticed this behavior as well. Thank you for providing the 'readLine' function! Would it be considered poor coding style to intercept the stream between readf and readln with the following statement? :

     auto catcher = readln.strip;

P.S. I love your book on D! :)

Cheers,

Gary Chike

On Monday, 20 June 2022 at 00:43:17 UTC, Ali Çehreli wrote:

Thank you for your input, Ali! Would it be appropriate to forego readf and read input as a string using readln ,benefiting from the strip function, then convert to their appropriate datatype as in the following example?:

module hello_world;

import std.stdio;
import std.string; // strip()
import std.conv; // to!int(),to!float()

void main() {
	writeln("Hello world from D!");
	write("What is your name? ");
	auto fname = readln.strip;
	writeln("It's so nice to meet you ", fname, "!");
	write("How old are you? ");
	auto age = to!int(readln.strip);
	write("What is your GPA? ");
	auto gpa = to!float(readln.strip);
	writeln("So, ", fname, ", you are ", age, " years old and your GPA is ",
		gpa, ".. stellar!");
}

Also I signed up with Educative.io to do your interactive D language lessons. It really goes so well with your book :)

Cheers,

Gary Chike

I should have qualified the above with: _ and I will be performing operations on the numeric datatype, since just outputting simply strings, as in the above example, would require nothing more than string data types. :)

module hello_world;

import std.stdio;
import std.string; // strip()
import std.conv; // to!int(),to!float()

void main() {
	writeln("Hello world from D!");
	write("What is your name? ");
	auto fname = readln.strip;
	writeln("It's so nice to meet you ", fname, "!");
	write("How old are you? ");
	auto age = to!int(readln.strip);
	write("What is your GPA? ");
	auto gpa = to!float(readln.strip);
	if (gpa > 4) {
		writeln("Sorry, 4 is the highest GPA ");
		gpa = 4; }
	writeln("So, ", fname, ", you are ", age, " years old and your GPA is ",
		gpa, ".. stellar!");
	writeln("Can you increase your GPA? ");
	if(gpa == 4) {
		writeln("Your GPA is already as high as it can be!");
	} else {		
		gpa = gpa > 3.5 ? 4 : (gpa + 0.5);
		writeln("If you study hard, your GPA will likely be ", gpa);
		age = age + 4;
		writeln("But that may take 4 years, and you will be ", age, " years old by that time.");
	}
}

On Monday, 20 June 2022 at 16:08:33 UTC, Ali Çehreli wrote:

Thank you so much for your input! Cheers! :)

On Monday, 20 June 2022 at 16:08:33 UTC, Ali Çehreli wrote:

It's interesting from my own experimentation and observation, comparing parse!int() vs to!int() For instance, I can formulate a statement such as this using to!int():
auto age = to!int(readln.strip());
but the same syntax using parse!int() would generate an error:
auto age = parse!int(readln.strip());
So, in order to use parse!int(), I would need to separate it into two statements with a variable acting as an intermediary:

auto input = readln();
auto age = parse!int(input);