Please, i need your help, I tried this:

write("Write p: ");
readln(p);
p = chomp(p);
writeln("Write q: ");
readln(q);
q = chomp(q);

but the result is:
Write p: Write q:

and doesn't pause to read keyboard input... what's wrong?

Thanks in advance!

On Friday, 27 March 2015 at 04:37:34 UTC, jonaspm wrote:
> Please, i need your help, I tried this:
>
> write("Write p: ");
> readln(p);
> p = chomp(p);
> writeln("Write q: ");
> readln(q);
> q = chomp(q);
>
> but the result is:
> Write p: Write q:
>
> and doesn't pause to read keyboard input... what's wrong?
>
> Thanks in advance!

http://dlang.org/phobos/std_stdio.html#.readln

Check the example, and you will see the problem. readln(p) doesn't read what was typed into p.

but readln(p); isn't supposed to read input and store it into p?

On Friday, 27 March 2015 at 04:37:34 UTC, jonaspm wrote:
> Please, i need your help, I tried this:
>
> write("Write p: ");
> readln(p);
> p = chomp(p);
> writeln("Write q: ");
> readln(q);
> q = chomp(q);
>
> but the result is:
> Write p: Write q:
>
> and doesn't pause to read keyboard input... what's wrong?
>
> Thanks in advance!

This works for me on Linux:
---

import std.stdio;
import std.string;
void main()
{
    char[] p, q;
    p.length=1024;
    q.length=1024;

    write("Write p: ");
    readln(p);
    p=p.chomp;

    write("Write q: ");
    readln(q);
    q=q.chomp;

    writeln; writefln("p=%s, q=%s", p,q);
}
---

bye,
lobo

On Friday, 27 March 2015 at 04:37:34 UTC, jonaspm wrote:
> Please, i need your help, I tried this:
>
> write("Write p: ");
> readln(p);
> p = chomp(p);
> writeln("Write q: ");
> readln(q);
> q = chomp(q);
>
> but the result is:
> Write p: Write q:
>
> and doesn't pause to read keyboard input... what's wrong?
>
> Thanks in advance!

The easiest to use is the form "<string> = readln()":

    write("Write p: ");
    auto p = readln().chomp();
    write("Write q: ");
    auto q = readln().chomp();

The second version, "<length> = readln(<buffer>)", goes something like:

    auto buf = new char[1024];
    write("Write p: ");
    string p = buf[0..readln(buf)].chomp().idup;
    write("Write q: ");
    string q = buf[0..readln(buf)].chomp().idup;

It allows to reuse a preallocated buffer for greater speed and finer allocation control.

Also worth noting, the best place for such questions in D.learn group:
http://forum.dlang.org/group/digitalmars.D.learn

Ivan Kazmenko.

On Friday, 27 March 2015 at 05:17:03 UTC, jonaspm wrote:
> but readln(p); isn't supposed to read input and store it into p?

Nope. Parameter is terminator character. Read string is returned from the function. So, it would be like:

string p = readln();

On 3/27/15 4:22 AM, tcak wrote:
> On Friday, 27 March 2015 at 05:17:03 UTC, jonaspm wrote:
>> but readln(p); isn't supposed to read input and store it into p?
>
> Nope. Parameter is terminator character. Read string is returned from
> the function. So, it would be like:
>
> string p = readln();

readln has an overload that looks like this:

size_t readln(C)(ref C[] buf, dchar terminator = '\x0a') if (isSomeChar!C && is(Unqual!C == C) && !is(C == enum));

Which is what the OP is using (possibly, he never defines p and q).

As for the error, assuming you have proper buffer types for p and q, it appears that your stdin is closed somehow. I think this is likely an environmental issue. Please post the full code and describe the environment if you need more help.

Your code works fine for me on OSX:

import std.stdio;
import std.string;

void main()
{
    char[] p;
    char[] q;
    write("Write p: ");
    readln(p);
    p = chomp(p);
    writeln("Write q: ");
    readln(q);
    q = chomp(q);

    writeln(p, " ", q);
}

RUN:

Write p: adb;lna;lhiser
Write q:
slisieleru
adb;lna;lhiser slisieleru

-Steve

module main;

import std.stdio;
import std.string;

int main(string[] args)
{
     int resp;
     char[] p, q;

     writefln("MENU DE OPCIONES");
     writefln("1) Modus Ponens");
     writefln("2) Modus Tollens");
     writefln("3) Silogismo Hipotetico");
     writefln("4) Salir");

	do{
	    writeln("Introduce la opcion que deseas: ");
	    readf(" %d", &resp);
	}while(resp<1 || resp>4);

	write("Write p:");
	readln(p);  // This is skipped. ¿?
	p = chomp(p);
	write("Write q:");
	readln(q);
	q = chomp(q);


     writeln("p: ",p); // Doesn't write anything.

     writeln("q: ",q); // Writes what you typed in the keyboard
back on readln();


	return 0;
}


This is the entire code.
Environment:
Windows 7 Home Premium x64
IDE: CodeBlocks 13.12
Compiler: Digital Mars D Compiler

On Saturday, 28 March 2015 at 03:07:31 UTC, jonaspm wrote:
> module main;
>
> import std.stdio;
> import std.string;
>
> int main(string[] args)
> {
>      int resp;
>      char[] p, q;
>
>      writefln("MENU DE OPCIONES");
>      writefln("1) Modus Ponens");
>      writefln("2) Modus Tollens");
>      writefln("3) Silogismo Hipotetico");
>      writefln("4) Salir");
>
> 	do{
> 	    writeln("Introduce la opcion que deseas: ");
> 	    readf(" %d", &resp);
> 	}while(resp<1 || resp>4);
>
> 	write("Write p:");
> 	readln(p);  // This is skipped. ¿?
> 	p = chomp(p);
> 	write("Write q:");
> 	readln(q);
> 	q = chomp(q);
>
>
>      writeln("p: ",p); // Doesn't write anything.
>
>      writeln("q: ",q); // Writes what you typed in the keyboard
> back on readln();
>
>
> 	return 0;
> }

The problem is that the `readf` call doesn't read the first line completely. It leaves the newline. The first `readln` call then picks up that newline and stops right there, resulting in an empty line.

I'm not sure how the `readf` could be changed to consume the newline. I tried " %d\n" and " %d ". They don't seem to do it.

But you can add a `readln();` after the `readf` call and it works.

You can clear the input stream:

> while(getchar() != '\n') {};

Or just use readln:

> int resp = readln.chomp.to!int;