How to send strings to a program, with a box open waiting for a string response?

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C++

I have a windows program that awaits for a login and password to keep running. I need to pass this information automatically, to it finish its job and start another.

I use createProcess to open this program, and waits for the response.

Right after I use keybd_event, to write the credential, and everything works fine.
But I'm not stisfyed, because this is a week solution, once someone opens a window while the programa is running the keybd_event will write on the opened window, and not in that one a wish to.

So how to send a string information to a program, and make it understand this string is the question that I wont to know. Any clues, and tips?

PS: In the code below I didn't put the keyboard class, because it is working fine.
I execute two times, in main, the funcition

executeCommandLine

to test if really one waits another finish its job to start.

Thanks very much for your time.
APS.

What I have tried:

// The class works fine.
// If correctely used, It write a string in the front window windows
#include "keyboard.h"

bool executeCommandLine(LPCSTR path, LPSTR cmdLine, DWORD &exitCode){
   PROCESS_INFORMATION processInformation = {0};
   STARTUPINFO startupInfo                = {0};
   startupInfo.cb                         = sizeof(startupInfo);

   BOOL result = CreateProcess(NULL, cmdLine,
                               NULL, NULL, FALSE,
                               NORMAL_PRIORITY_CLASS | CREATE_NO_WINDOW,
                               NULL, NULL, &startupInfo, &processInformation);

   if (!result){
      // CreateProcess() failed
      // Get the error from the system
      LPVOID lpMsgBuf;
      DWORD dw = GetLastError();
      FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
                    NULL, dw, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), (LPTSTR) &lpMsgBuf, 0, NULL);

      // Display the error
      string strError = (LPTSTR) lpMsgBuf;
      //TRACE(_T("::executeCommandLine() failed at CreateProcess()\nCommand=%s\nMessage=%s\n\n"), cmdLine, strError);

      // Free resources created by the system
      LocalFree(lpMsgBuf);

      // We failed.
      return FALSE;
   }
   else{
// Here is the moment I use the keyboard to write the login and password.
// It works fine, but it's a week solution, a need to send 2 different strings in two //dialogue boxes that opens one after another (once the ENTER key was pressed, in both //cases) when the process starts: one with the LOGIN and other with the PASSWORD
	   	keyboard keybd;
	   	Sleep(3000);
	   	keybd.text("LOGIN");
	   	keybd.press_enter(TRUE);
	   	Sleep(200);
	   	keybd.text("PASSWORD");
	   	keybd.press_enter(TRUE);

      // Successfully created the process.  Wait for it to finish.
      WaitForSingleObject( processInformation.hProcess, INFINITE );

      // Get the exit code.
      result = GetExitCodeProcess(processInformation.hProcess, &exitCode);

      // Close the handles.
      CloseHandle( processInformation.hProcess );
      CloseHandle( processInformation.hThread );

      if (!result){
         return FALSE;
      }

      // We succeeded.
      return TRUE;
   }
}

int main() {
	LPSTR command = LPSTR("command line text");
	DWORD exitCode;
// executeCommandLine two times.
// to verfy if the first waits for the second. It works fine.
	executeCommandLine(NULL, command, exitCode);
	executeCommandLine(NULL, command, exitCode);
	return 0;
}