capture console application output into textbox

When you say "output text to the console" are you specifying you want to run the console app to output to an ACTUAL console window rather than redirecting its output to a file?

You can run a console app and redirect its output to a file, then use your c# app to read the file  (there CAN be buffering issues here, though, depending on how often the console app flushes its output).

The output should be redirected to the c# app,  but not displayed to the console(or better, do not display the console app while running). I want to do this without files.
Again:
1. the c# launches the console app
2. the console app DOES NOT display anything, it should run "hidden"
3. the console app should redirect its output to the c# app.

Sounds like a job for a pipe!

Take a look at the docs for "anonymous pipes"

Even simpler, you can use the Process.StartInfo  to redirect the standard output.

From MSDN docs:

// Start the child process.
 Process p = new Process();
 // Redirect the output stream of the child process.
 p.StartInfo.UseShellExecute = false;
 p.StartInfo.RedirectStandardOutput = true;
 p.StartInfo.FileName = "Write500Lines.exe";
 p.Start();
 // Do not wait for the child process to exit before
 // reading to the end of its redirected stream.
 // p.WaitForExit();
 // Read the output stream first and then wait.
 string output = p.StandardOutput.ReadToEnd();
 p.WaitForExit();

In your case, of course, you sound like you'd rather to the occasional .ReadLine or even asynchronous stream I/O to send your text to your textbox, not a ReadToEnd.

Great, but how do I know when to do the Readline, if the console application outputs some text from time to time?

That's what I meant with the asynchronous stream I/O.

You can do a "BeginRead" on the stream and specify a callback function to call when you get some text.

Sounds nice. Could you please give me an example? I never used callbacks so I don't know how to use them for capturing the output, as you say
Thank you

Sure...let's say we have this as our console app...
Just generates a bunch of lines with random 0-10 second intervals between.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
 
namespace OutputGenerator
{
    class Program
    {
        static void Main(string[] args)
        {
            Random generator = new Random();
            int max = 10 + generator.Next(500);
            for (int i = 0; i < generator.Next(500); i++)
            {
                int wait = generator.Next(10);
                Console.WriteLine(i.ToString() + " out of " + max.ToString() + " items - " + wait.ToString());
                Thread.Sleep(1000 * wait);
            }
        }
    }
}

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Thank you very much both of you.You helped me a lot.