You can use this script in your game to create level codes!
Warning!!! scripts are very long, took me many hours to create these! Warning!!!
No credit needed all thought it would be nice!!!
made by koaladude

Load Button Script-use a left click or silmilar, on an object to bring up a field to enter a code

level2 = "inesrt the passcodes here"
level3 = ""
level4 = ""
level5 = ""
level6 = ""
level7 = ""
level8 = ""
level9 = ""
level10 = ""
level11 = ""
level12 = ""
level13 = ""
level14 = ""
level15 = ""
level16 = ""
level17 = ""
level18 = ""
level19 = ""
level20 = ""
level21 = ""
level22 = ""
level23 = ""
level24 = ""
level25 = ""

message_background(whatever background for the message, or omit this pert for gamemaker messagebox)
message_text_font(whatever fon that you want,14,c_orange,or other color,0)
a =  get_string('Enter the level password','')


-use this to correspond to the levels in you game, duplicate for every level inserting the level name and code

if a = level2-or other level
{message_background(message background or omit)
message_text_font(your messageg box font,14,random($FFFFFF),0)
show_message("Level 2-or other level- access code entered successfully!")
room_goto(Room2-or other level)}

-insert at end of all the level's code

else
{message_background(your message bakground)
message_text_font(your message font,14,c_red,0)
show_message("Wrong Code!!")}


------------------------------------------------------------------------



-insert a finish line object and assign a collision to the charachter colliding with the finish line
-use this to display level code at the end of a level after the yhave beaten it

message_background(your message background or omit)
message_text_font(your message font,14,random($FFFFFF),0)
if room = Room2-or wahtever level 
show_message("Level 2 -or whatever level Completed!#Level code is whatever that corresponds to that level code")
room_goto_next()