Hey I have just started programming not so long ago and I was thinking about making a Zork like game but I keep getting stuck. I really want it to have text input like Zork so the player can type for example "Hello" and the game will respond with "Hi" or "Greetings". can any one help me with this Thanks.

Well, the actual implementation depends on the language you are using, but the basic idea is:
if(playerInput == "hello")
{
Display("Greetings!");
}
else if(playerInput == "goodbye")
{
Display("Cya later!");
}
else
{
Display("I don't recognize that sentence.");
}


To further expand on it, you could add verbs and nouns:

Words = BreakIntoWords(playerInput);
if(FirstWord == "Use")
{
if(SecondWord == "Banana" AND PlayerHas("banana"))
{
Display("You threw the banana at the Rhino in disgust!")
}
else if(SecondWord == "Apple" AND PlayerHas("apple"))
{
Display("You fed the Rhino your apple, and he munches on it thoughtfully.")
Display("Rhino: 'Mmm, that was delicious. Here, you can have my extra backup horn as thanks.")

GivePlayer("Rhino Horn");
Display("Dun dun dun duhhh! You got the Rhino Horn! You can now go gore some Kangaroos.")
}
else if(SecondWord == "")
{
Display("What do you want to use?")
}
else
{
Display("You don't have any " + SecondWord)
}
}
else if(FirstWord == "Take")
{
if(ExistsInRoom(SecondWord))
{
Display("You take the " + SecondWord)
GivePlayer(SecondWord);
RemoveFromRoom(SecondWord);
}
else if(SecondWord == "")
{
Display("What do you want to take?")
}
else
{
Display("You can't take any " + SecondWord)
}
}
else
{
Display("I don't know what you said. Could you try: 'Use', 'Take', 'Look', 'Go', or 'Talk'?")
}

Required knowledge:

• 'if()' statements
  
• 'if else()' statements
  
• 'else' statements
  
• 'while' loops
  
• What kind of food rhinos like
  
• Strings
  
• String comparison
  

Tips:

• If you convert player input to lowercase before comparing it, you only have to check for "the word", and you automaticly handle "The Word", "THE WORD", and "ThE WoRd".
  
• If you break things into small functions, you can make your program more stable, easy to read, easy to expand, and also save alot of typing.
  
• Any time you find yourself copying and pasting your code into multiple places, turn it into a function instead.
  
• If you want to do something, and find out that you can't, instead of getting frustrated, ask yourself how you can use the limitation to improve your game, or how you can work around the limitation.
  
• A quick google search shows that Rhinos actually do like apples. Odd.
  
• Quick google searches can also answer most problems you encounter - but make sure you actually understand the answer, don't just copy and paste the answer.
  
• A sense of humor in your game might help you feel better about the lack of graphics.
  
• Everyone knows that mules have a terrific sense of humor... which is why they make such great game designers.
  
• Using graph paper (or plain computer paper and a ruler) map out the rooms, location of items, and the required order of getting/using each item, before you actually start adding anything other than test rooms.
  
• Hard code everything if you have to. Use global variables if you need to.
  
• Aim small for your first game (20 rooms top). For your second game, figure out how to load text files, and make rooms, items, npcs, and the connections between rooms be as much as possible controlled by files and not hard-coded. Also try to not use a single global variable. Consider it a challenge or puzzle to solve.
  

Hey and thanks guys Im using c++ I forgot to mention that sorry.

If you could use .net i'm sure a dictionary would work fine as well. http://msdn.microsoft.com/en-us/library/xfhwa508.aspx

To me, if you're using C++ at first I would say string comparison as well. (From if this == this) or possibly with an array? Just store an array of commands for a subset of the program. (ie. Attacking, moving, talking, etc)

I'd actually do not direct string comparison. It's easy in the beginning, but will grow too fast to be managable.

I wouldn't use it either, but I don't know the OP's skill level, and am guessing from his post he hasn't yet mastered basic comparison. I could be wrong though!

[quote name='Endurion' timestamp='1347003698' post='4977518']
I'd actually do not direct string comparison. It's easy in the beginning, but will grow too fast to be managable.

I wouldn't use it either, but I don't know the OP's skill level, and am guessing from his post he hasn't yet mastered basic comparison. I could be wrong though!
[/quote]

Instead of direct comparison what should be used? Because that's what pops into my head first when i think of string and comparing.

For handling alot of string comparisons std::map abstracts it better, making it easier to make your game data-driven and less hardcoded.

Probably std::map<std::string, scriptCallbackFunction>
Or std::map<std::string, classThatHandlesAction>
Or maybe using C++11 lambdas: std::map<std::string, lambdasCallback>,but in this situation that's unlikely.

Then you could do:
actionMap.push_back(std::make_pair("Use", UseActionHandler(pointerToPlayerData, pointerToWorldData)));
actionMap.push_back(std::make_pair("Go", GoActionHandler(pointerToPlayerData, pointerToWorldData)));
actionMap.push_back(std::make_pair("Say", SayActionHandler(pointerToPlayerData, pointerToWorldData)));
actionMap.push_back(std::make_pair("Get", GetActionHandler(pointerToPlayerData, pointerToWorldData)));
actionMap.push_back(std::make_pair("Attack", AttackActionHandler(pointerToPlayerData, pointerToWorldData)));
actionMap.push_back(std::make_pair("Run", RunActionHandler(pointerToPlayerData, pointerToWorldData)));
actionMap.push_back(std::make_pair("Climb", ClimbActionHandler(pointerToPlayerData, pointerToWorldData)));


You could also easily handle synonyms.
actionMap.push_back(std::make_pair("Say", SayActionHandler(pointerToPlayerData, pointerToWorldData)));
actionMap.push_back(std::make_pair("Speak", SayActionHandler(pointerToPlayerData, pointerToWorldData)));
actionMap.push_back(std::make_pair("Talk", SayActionHandler(pointerToPlayerData, pointerToWorldData)));

actionMap.push_back(std::make_pair("Go", GoActionHandler(pointerToPlayerData, pointerToWorldData)));
actionMap.push_back(std::make_pair("Walk", GoActionHandler(pointerToPlayerData, pointerToWorldData)));
actionMap.push_back(std::make_pair("Head", GoActionHandler(pointerToPlayerData, pointerToWorldData)));


Or maybe use Regex instead (which is also abstract comparison of complex strings), and use a single action handler.
Or just map the word "Go" to a script function that handles the action.
actionMap.push_back(std::make_pair("Go", "handle_go"));

if(actionMap.contains(playerFirstWord))
{
functionName = actionMap[playerFirstWord];
CallScriptFunction(functionName, inputWords, playerPtr, worldPtr);
}
else
{
Output("I don't recognize " +playerFirstWord + ". Did you mean: " + actionMap.keys());
}

This doesn't keep you from having to write the logic, but it makes the logic easier to alter or expand during development, and easier to understand than 1500 lines of if(), else-if(), spaghetti going several scopes deep, and when and where you need actual if() statements, you only have them grouped together in twos and threes based on context, not hundreds.

It also makes it easier to create things like:
"Give to Bob the Monkey" -> You gave Bob, the Friendly Monkey you found. Bob looks at you quizzically.

'Give' goes to GiveActionHandler or script function, parses 'to' if present and discarded it, and using the pointer to the world, finds what NPCs exist in the room the player is in, finds a NPC named 'Bob' (otherwise outputting, "You don't see anyone named Bob around here"), parses and discards 'the' if present. Then using the pointer to the player's data, checks if the player has an item called 'Monkey' (otherwise outputting, "You don't have a Monkey"), and passes the text "Monkey" to Bob's script file for processing.

Bob's script file looks like this:
HandleLook()
{
Output("Bob stares back at you.")
}

HandleTalk()
{
//...
}

HandleGive(itemName, playerPtr, worldPtr)
{
if(itemName == "Monkey")
{
playerPtr.RemoveItem(itemName);
worldPtr.AddNPC("MonkeyNPC", worldPtr->GetCurrentRoom());
Output("Bob: You found Fibi! Oh thank you, " + playerPtr.name + "! I looked all over for her.")
Output("Bob: Here, take my spare scuba gear as thanks. You may find it comes in handy.")

playerPtr.GiveItem("Scuba gear");
}
else
{
Output("Bob: Uh, thanks, but I'm not interested in " + itemName + "s at the moment.');
}
}

This would be my first attempt, anyway. When working on the game, a better architecture may come to mind once I encounter the strengths and limitations of this approximation, having never worked on this type of game before (aside from a few attempts when first starting out as a programmer seven years ago).

Essentially you're trying to write something that parses English (or whatever language), which is challenging as human speech is generally not strictly rule-based and is sometimes ambiguous. Generally assume that there will be limitations on your program's ability to parse text, so you will have to draw a line somewhere.

On to practicalities, the guys here have suggested some good stuff. The solution depends upon your programming skill and whether you just wan results or want to do it yourself. The interactive fiction engines mentioned do a pretty good job of interpreting text.

If you want to write your own you can do what the guys mentioned above. Or you could take the more complex route and create a grammar and parse the text into trees based on the grammars and see which fits best, for example the rules "[verb] [noun phrase]" (e.g. "go north") and "[noun]" (e.g. "north"). If you want to be really smart, interpret the nouns (and maybe even verbs) in a context-sensitive way, e.g. if they say "pick up the sword" interpret sword as a nearby sword that they are not holding. You can rule out interpretations if there are no matching nouns in the context.