Ok, well I got a bit carried away here and expanded the code considerably regarding functions . I moved all the display items into their own functions and also moved the bulk of the input processing into a function called ProcessUserInput.
So the game now allows 5 guesses and decrements the lives each time the user gets the word wrong (still just a simple equality check on this for now). The player’s guess, result and life count are all displayed following each guess and once you either guess correctly or run out of lives the program then prompts for input to restart or quit and implements that.
Not sure if setting GIsRequestingExit to true is the correct way of exiting the Unreal Engine as it closed my Editor too the first time I tried it!!! However, when running the game standalone it seems fine … I know, I probably should have waited as I’m sure you’ll be covering that later 
My header file additions:
// Your declarations go below!
private:
FString HiddenWord;
FString CurrentWordGuess;
bool bHelpCalled;
bool bNewWord;
bool bHasGuessed;
bool bInitGame;
bool bContinuePlay;
int32 LivesLeft;
void DisplayWelcome();
void DisplayHelp();
void InitGame();
void ProcessUserInput(const FString& Input);
void DisplayInstruction();
void DisplayGuess(const FString& Guess);
void DisplayLivesRemaining(int32 Lives);
void DisplayContinueGamePrompt();
and my code:
#include "BullCowCartridge.h"
void UBullCowCartridge::BeginPlay() // Called by Unreal Engine when the game starts
{
Super::BeginPlay();
InitGame();
}
void UBullCowCartridge::OnInput(const FString& Input) // When the player hits enter
{
ClearScreen();
ProcessUserInput(Input);
}
void UBullCowCartridge::InitGame()
{
// Initialise variables
HiddenWord = TEXT("Place"); // Always encose literal strings in a TEXT macro to ensure native Unicode encoding.
bHelpCalled = false; // Flag to indicate if DisplayHelp had previously been called
bNewWord = false; // Flag to indicate its a new word
bHasGuessed = false; // Flag to indicate the user has provided a guess
bInitGame = false; // Flag to indicate start of a new game
bContinuePlay = true; // Flag to indicate play should continue
LivesLeft = 5;
DisplayWelcome();
}
void UBullCowCartridge::ProcessUserInput(const FString& Input)
{
// Handle the ContinueGamePrompt user input
if (!bContinuePlay)
{
if (Input == TEXT("r"))
{
InitGame();
bContinuePlay = true;
return;
}
else if (Input == TEXT("q"))
{
// Quit game
GIsRequestingExit = true;
}
else
{
DisplayContinueGamePrompt();
return;
}
}
DisplayInstruction();
// If user previously called help then display the previously stored word guess
if (bHelpCalled)
{
if (CurrentWordGuess != "")
{
DisplayGuess(CurrentWordGuess);
DisplayLivesRemaining(LivesLeft);
}
// Reset our help called flag
bHelpCalled = false;
return;
}
// So long as something has been typed
if (Input != "")
{
// If user requested help
if (Input == TEXT("help"))
{
DisplayHelp();
// Set our help called flag
bHelpCalled = true;
}
else
{
// Store the current word guess incase the user subsequently requests help or just hits enter and we need to restore the guess
CurrentWordGuess = Input;
bHasGuessed = true;
// Test to see if the guess is correct or not
if (Input == HiddenWord)
{
// Display the users latest guess
DisplayGuess(Input);
PrintLine(TEXT("Correct. You Win!"));
DisplayContinueGamePrompt();
bContinuePlay = false;
CurrentWordGuess = "";
bNewWord = true;
bHasGuessed = false;
}
else
{
// Decrement the number of lives left
--LivesLeft;
DisplayGuess(Input);
if (LivesLeft == 0)
{
PrintLine(TEXT("You have no lives left"));
DisplayContinueGamePrompt();
bContinuePlay = false;
}
else
{
PrintLine(TEXT("Incorrect. You lose a life"));
PrintLine(TEXT("Please try again"));
DisplayLivesRemaining(LivesLeft);
}
}
}
}
else if (bHasGuessed)
{
// If the user has previously guessed but has just pressed Enter then print previous guess
DisplayGuess(CurrentWordGuess);
DisplayLivesRemaining(LivesLeft);
}
}
void UBullCowCartridge::DisplayWelcome()
{
PrintLine(TEXT("Welcome to the Bulls and Cows game\n"));
PrintLine(TEXT("Press Enter to continue"));
}
void UBullCowCartridge::DisplayHelp()
{
ClearScreen();
PrintLine(TEXT("The game is a guess the hidden word game."));
PrintLine(TEXT("The hidden word will always be an ISOGRAM,"));
PrintLine(TEXT("that is a word with no repeating letters."));
PrintLine(TEXT("Any correct letters in the right position"));
PrintLine(TEXT("will score you BULLS, any correct letters"));
PrintLine(TEXT("in the wrong position will score you COWS"));
PrintLine(TEXT("and any wrong letters score nothing."));
PrintLine(TEXT("You will have so many tries in order to "));
PrintLine(TEXT("guess the word correctly and win the game."));
PrintLine(TEXT("Press Enter to return to the game."));
}
void UBullCowCartridge::DisplayInstruction()
{
PrintLine(TEXT("Type help and press Enter for a basic"));
PrintLine(TEXT("description of the game and rules.\n"));
PrintLine(TEXT("Otherwise guess the 5 letter word ...\n"));
}
void UBullCowCartridge::DisplayGuess(const FString& Guess)
{
PrintLine("You guessed: " + Guess);
}
void UBullCowCartridge::DisplayLivesRemaining(int32 Lives)
{
PrintLine(TEXT("You have " + FString::FromInt(LivesLeft) + TEXT(" lives remaining")));
}
void UBullCowCartridge::DisplayContinueGamePrompt()
{
PrintLine(TEXT("To restart type 'r' and Enter"));
PrintLine(TEXT("To quit type 'q' and Enter"));
}