'by chatgpt
DIM rooms$(20), descriptions$(20)
DIM inventory$(20), inventoryCount AS INTEGER
DIM playerRoom AS INTEGER
DIM command$, verb$, obj$
DIM items$(10), itemLocations(10) AS INTEGER
DIM lightSource AS INTEGER, score AS INTEGER, grueActive AS INTEGER

' Define rooms
rooms$(0) = "Entrance Hall"
descriptions$(0) = "You are in an old entrance hall. There is a door to the north."
rooms$(1) = "Dark Corridor"
descriptions$(1) = "A dark, damp corridor. It smells musty. There is a door to the south and stairs to the east."
rooms$(2) = "Basement"
descriptions$(2) = "A damp basement with an old chest. The stairs lead back west."
rooms$(3) = "Cave Entrance"
descriptions$(3) = "A rocky entrance to a deep cave. The air feels heavy."
rooms$(4) = "Underground River"
descriptions$(4) = "A fast-flowing river blocks the way. You might need a boat."
rooms$(5) = "Treasure Chamber"
descriptions$(5) = "A hidden chamber filled with ancient treasures."
rooms$(6) = "Twisting Maze"
descriptions$(6) = "A confusing maze of passages. You hear strange noises."
rooms$(7) = "Deep Cavern"
descriptions$(7) = "A cavern shrouded in darkness. Something is here..."

' Define items
items$(0) = "KEY": itemLocations(0) = 2 ' Key is in the basement
items$(1) = "CHEST": itemLocations(1) = 2 ' Chest is in the basement
items$(2) = "LANTERN": itemLocations(2) = 0 ' Lantern is in the entrance hall
items$(3) = "BOAT": itemLocations(3) = 4 ' Boat is at the underground river
items$(4) = "GOLD": itemLocations(4) = 5 ' Gold is in the treasure chamber

playerRoom = 0
inventoryCount = 0
lightSource = 0
grueActive = 1
score = 0

DO
   CLS
   PRINT "Location: "; rooms$(playerRoom)
   
   ' Check if the room is dark and Grue is active
   IF playerRoom = 7 THEN
       IF lightSource = 0 THEN
           PRINT "It is pitch black!"
           PRINT "A sinister presence is near..."
           PRINT "You have been eaten by a Grue!"
           EXIT DO
       END IF
   END IF
   
   PRINT descriptions$(playerRoom)
   
   ' Show items in the current room
   FOR i = 0 TO 4
       IF itemLocations(i) = playerRoom THEN PRINT "You see: "; items$(i)
   NEXT i
   
   PRINT "What do you want to do?"
   INPUT command$
   command$ = UCASE$(command$)
   
   ' Parse input
   verb$ = LEFT$(command$, INSTR(command$, " ") - 1)
   obj$ = MID$(command$, INSTR(command$, " ") + 1)
   
   SELECT CASE verb$
       CASE "GO"
           SELECT CASE obj$
               CASE "NORTH": IF playerRoom = 0 THEN playerRoom = 1
               CASE "SOUTH": IF playerRoom = 1 THEN playerRoom = 0
               CASE "EAST": IF playerRoom = 1 THEN playerRoom = 2
               CASE "WEST": IF playerRoom = 2 THEN playerRoom = 1
               CASE "DOWN": IF playerRoom = 2 THEN playerRoom = 3
               CASE "CROSS": IF playerRoom = 4 AND lightSource = 1 THEN playerRoom = 5
               CASE "MAZE": IF playerRoom = 3 THEN playerRoom = 6
               CASE "CAVERN": IF playerRoom = 6 THEN playerRoom = 7
               CASE ELSE: PRINT "You can't go that way."
           END SELECT
       
       CASE "TAKE"
           FOR i = 0 TO 4
               IF items$(i) = obj$ AND itemLocations(i) = playerRoom THEN
                   inventory$(inventoryCount) = obj$
                   inventoryCount = inventoryCount + 1
                   itemLocations(i) = -1 ' Remove item from room
                   PRINT "You take the "; obj$; "."
                   IF obj$ = "GOLD" THEN score = score + 10
                   IF obj$ = "LANTERN" THEN lightSource = 1
                   EXIT FOR
               END IF
           NEXT i
       
       CASE "OPEN"
           IF obj$ = "CHEST" AND playerRoom = 2 THEN
               PRINT "You open the chest and find an old letter."
           ELSE
               PRINT "You can't open that."
           END IF
       
       CASE "INVENTORY"
           PRINT "You are carrying:"
           IF inventoryCount = 0 THEN PRINT "Nothing."
           FOR i = 0 TO inventoryCount - 1
               PRINT inventory$(i)
           NEXT i
       
       CASE "SCORE"
           PRINT "Your current score: "; score
       
       CASE "QUIT"
           EXIT DO
       
       CASE ELSE
           PRINT "Unknown command."
   END SELECT
   
   PAUSE 500
LOOP

PRINT "Game over."

PRINT, INPUT, IF...THEN...ELSE...END IF, WHILE...WEND, SUB, FUNCTION...END FUNCTION, DIM, TYPE (struct), (Arrays), PRINT USING.

What built-in functions in FreeBasic are there?

Mathematical Functions

Abs(x): Returns the absolute value of x.
Sqr(x): Returns the square root of x.
Sin(x), Cos(x), Tan(x): Trigonometric functions.
Log(x): Returns the natural logarithm of x.
Exp(x): Returns e raised to the power of x.
Rnd(): Returns a random number between 0 and 1.
Int(x): Returns the integer part of x.

String Functions

Len(s): Returns the length of string s.
Mid(s, start, length): Extracts a substring from s.
LCase(s) and UCase(s): Converts a string to lowercase or uppercase.
InStr(string1, string2): Returns the position of the first occurrence of string2 in string1.
Trim(s): Removes leading and trailing whitespace from s.

File Handling Functions

Open: Opens a file for reading, writing, or appending.
Close: Closes an open file.
EOF(file number): Returns true if the end of the file is reached.
Input#: Reads formatted data from a file.
Print#: Writes formatted data to a file.

Type-related Functions

Typeof(var): Returns the data type of the variable var.
CStr(var): Converts var to a string.
CInt(var): Converts var to an integer.

Miscellaneous Functions

Sleep(milliseconds): Pauses the program for a specified number of milliseconds.
GetTime: Returns the current system time.
GetDate: Returns the current system date.

' Simple Text Adventure Game in FreeBASIC
Option Base 1
Dim currentRoom As Integer
Dim inventory As String
Dim rooms(7) As String
Dim connections(7, 4) As Integer
Dim action As String
Dim item As String
Dim direction As String
Dim nextRoom As Integer
Dim grueEncountered As Integer


' Room descriptions with exits
rooms(1) = "You are in a dimly lit chamber. There is a door to the north leading to Room 2."
rooms(2) = "You enter a bright room filled with treasure. There's a shimmering gold coin here. Exits: south to Room 1, east to Room 3."
rooms(3) = "You find yourself in a dark cave. A faint light flickers to the east. Exits: west to Room 4, south to Room 2."
rooms(4) = "You are in a library filled with dusty books. There's a magical scroll on a table. Exits: east to Room 5, west to Room 3."
rooms(5) = "You step into a garden with beautiful flowers. A rusty key lies on the ground. Exits: west to Room 4, east to Room 6."
rooms(6) = "You are in a grand hall with a large chandelier. An old lamp sits on a pedestal. Exits: west to Room 5, east to Room 7."
rooms(7) = "You've reached the throne room. A mysterious potion rests on the throne. Exits: west to Room 6."

' Room connections
connections(1, 1) = 2 ' North to Room 2
connections(1, 2) = 0 ' East
connections(1, 3) = 0 ' South
connections(1, 4) = 0 ' West

connections(2, 1) = 0 ' North
connections(2, 2) = 3 ' East to Room 3
connections(2, 3) = 1 ' South to Room 1
connections(2, 4) = 0 ' West

connections(3, 1) = 0 ' North
connections(3, 2) = 0 ' East
connections(3, 3) = 2 ' South to Room 2
connections(3, 4) = 4 ' West to Room 4

connections(4, 1) = 0 ' North
connections(4, 2) = 5 ' East to Room 5
connections(4, 3) = 3 ' South to Room 3
connections(4, 4) = 0 ' West

connections(5, 1) = 0 ' North
connections(5, 2) = 6 ' East to Room 6
connections(5, 3) = 4 ' South to Room 4
connections(5, 4) = 0 ' West

connections(6, 1) = 0 ' North
connections(6, 2) = 7 ' East to Room 7
connections(6, 3) = 5 ' South to Room 5
connections(6, 4) = 0 ' West

connections(7, 1) = 0 ' North
connections(7, 2) = 0 ' East
connections(7, 3) = 6 ' South to Room 6
connections(7, 4) = 0 ' West

If True = 0 Then True = 1

' Main game loop
currentRoom = 1
inventory = ""
grueEncountered = False

While True
   Cls
   
   ' Check for Grue in the dark cave (Room 7)
   If currentRoom = 7 And Not instr(inventory, "old lamp") Then
       grueEncountered = True
       Print "A Grue appears from the shadows! You have been eaten by the Grue!"
       End
   End If

   ' Print the room description
   Print rooms(currentRoom)

   ' Check for items
   Select Case currentRoom
       Case 2
           Print "You see a shimmering gold coin."
       Case 4
           Print "You see a magical scroll on the table."
       Case 5
           Print "You see a rusty key on the ground."
       Case 6
           Print "You see an old lamp on the pedestal."
       Case 7
           Print "You see a mysterious potion on the throne."
   End Select

   ' Check win condition using Instr
       nItems=5
       If Instr(inventory, "gold coin") = 0 then nItems=nItems-1
       If Instr(inventory, "magical scroll") = 0 then nItems=nItems-1
       If Instr(inventory, "rusty key") = 0 then nItems=nItems-1
       If Instr(inventory, "old lamp") = 0 then nItems=nItems-1
       If Instr(inventory, "mysterious potion") = 0 then nItems=nItems-1
       if nItems=5 then
         Print "Congratulations! You have collected all the items and won the game!"
         End
       End If

   Print "What do you want to do? (north, east, south, west, take [item], inventory, quit)"
   Input action

   ' Handle input
   If action = "quit" Then
       End
   ElseIf mid$(action, 1, 4) = "take" Then
       item = mid$(action, 6)
       If currentRoom = 2 And item = "coin" Then
           inventory = inventory + "gold coin, "
           Print "You took the gold coin."
       ElseIf currentRoom = 4 And item = "scroll" Then
           inventory = inventory + "magical scroll, "
           Print "You took the magical scroll."
       ElseIf currentRoom = 5 And item = "key" Then
           inventory = inventory + "rusty key, "
           Print "You took the rusty key."
       ElseIf currentRoom = 6 And item = "lamp" Then
           inventory = inventory + "old lamp, "
           Print "You took the old lamp."
       ElseIf currentRoom = 7 And item = "potion" Then
           inventory = inventory + "mysterious potion, "
           Print "You took the mysterious potion."
       Else
           Print "You can't take that."
       End If
   ElseIf action = "inventory" Then
       Print "You have: "; inventory
   Else
       Select Case action
           Case "north": direction = "north"
           Case "east": direction = "east"
           Case "south": direction = "south"
           Case "west": direction = "west"
           Case Else: direction = ""
       End Select

       If direction <> "" Then
'            nextRoom = connections(currentRoom, direction = "north" * 1 + direction = "east" * 2 + direction = "south" * 3 + direction = "west" * 4)
           dirNum=(direction = "north") * 1 + (direction = "east") * 2
           dirNum=dirNum + (direction = "south") * 3 + (direction = "west") * 4
           nextRoom = connections(currentRoom, dirNum)

           If nextRoom > 0 Then
               currentRoom = nextRoom
           Else
               Print "You can't go that way."
           End If
       End If
   End If

   Pause 1000' Pause for a moment
Wend