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Local/Global Variables

You might have had this problem before: FOR I=0 TO 3 TEST NEXT DEF TEST FOR I=0 TO 7 PRINT "A"; NEXT ENDThe FOR I=0 TO 3 code only runs once, since I becomes 8 after TEST is called. The way to avoid this is by using local variables. These are special variables in functions that won't affect global variables (variables outside of functions) with the same name. To use local variables inside functions, VAR* them within the function: X=2 'global DEF TEST VAR X=4 'doesn't affect the global variable "X" END If you want to access global variables, you must use the variable outside the function first (be sure to VAR your global variables before any DEFs) Right: VAR X=2 DEF TEST X=3 ENDWrong: DEF TEST X=3 'accesses the local variable since the global one hasn't been used yet END VAR X=2 *VAR and DIM are exactly the same; most people use VAR for regular variables and DIM for arrays. DEF TEST1 A=7 'local (don't do this, use VAR) END A=3 'global DEF TEST2 A=7 'global END DEF TEST3 VAR A=7 'local END DEF TEST4 A A=7 'local END DEF TEST5 OUT A A=7 'local END Local variables in SB are pretty weird Whether a variable in a function is local depends on whether the variable was used outside the function before (on a earlier line) 1: VAR/DIM doesn't actually do anything (VAR I=1 is equivalent to I=1). OPTION STRICT will not change this, it just causes an error if you don't use VAR the first time 2: There can be different variables with the same name (one global version, and multiple local versions (inside functions)) DEF TEST A=2 'local END DEF TEST2 PRINT A 'different local variable END A=7 'global TEST 'only sets its own copy of the variable (does nothing) TEST2 'prints 0 3: During pre-compilation, SB reads the code from top to bottom to look for variables OPTION STRICT GOTO @SKIP VAR X 'SB sees this even though it never gets run. (This only affects OPTION STRICT) @SKIP X=1 'does not cause an error 4: Variables defined inside of functions are normally local see example 2 5: Variables outside of functions are always global DEF TEST A=7 'local variable END A=3 'global TEST 'only sets its own local variable "A" PRINT A 'prints 3 5: Once a global variable has been defined, all variables after it with that name will be global (including inside DEFs) DEF TEST1 PRINT A 'local END A=4 'global DEF TEST2 PRINT A '<-global! END 'What matters is the order of the DEFs, not the order that functions are run! TEST2 'prints 4 TEST1 'prints 0 (and in case you're wondering, function arguments and OUT returns are always local) (also, different slots use completely separate variables, so don't worry about that)
Author
12Me21
Updated
Rating
2 votes
Categories
Keywords
  • local
  • global
  • DEF
  • variable
  • function
4 Comment(s) kldck_hul kldck_hul First Month Joined in the very first month of SmileBASIC Source Website Scholar Received for knowing a great deal about programming topics Achievements Zelda Is Awesome! I love The Legend Of Zelda! Express Yourself So I noticed that your points 1 and 2 are incorrect... The code below will use only one variable: VAR A=7 'global DEF TEST A=2 'not local END DEF TEST2 PRINT A 'the same global END TEST 'sets the global TEST2 'prints 2 This has to do with where the statement defining the global is placed. The commands in your example are defined before the global, and as such, don't know that A is a global they can assign to. It hasn't been declared yet. MZ952 MZ952 Intermediate Programmer I can make programs, but I still have trouble here and there. Programming Strength Drawing I like to draw! Hobbies Reading I like to read books! Hobbies This is very useful to know! So, if I keep all my DEF functions at the top of the program, I can avoid having the functions' variables affecting outside variables? I wonder why not just keep all variables inside DEF functions local, or why not let the programmer specify it with a command like COMMON. kldck_hul kldck_hul First Month Joined in the very first month of SmileBASIC Source Website Scholar Received for knowing a great deal about programming topics Achievements Zelda Is Awesome! I love The Legend Of Zelda! Express Yourself Its very easy to keep your local and global variables from mixing, even if they come after those global variables. You just have to redeclare the variable in the DEF block using VAR. I recommend ALWAYS using VAR the first time a variable is seen. Using VAR does do something, and I believe 12Me21 made an honest mistake and missed it. Take this code as an example: DEF TEST INC iter% 'Hasn't been declared as global yet 'will create a local PRINT "1:",iter% END VAR iter% = 42 'Declare iter% as a global DEF TEST2 INC iter% 'Will increment the global variable 'because it was declared prior PRINT "2:",iter% END DEF TEST3 VAR iter% 'Shadow the global INC iter% 'Will increment the local 'because it is declared inside PRINT "3:",iter% END DEF TEST4 INC iter% 'Has been declared as global PRINT "4:",iter% END TEST;TEST2;TEST3;TEST4 Edit: more complete example 12Me21 12Me21 Admin Syntax Highlighter Received for creating the code syntax highlighter on SBS Night Person I like the quiet night and sleep late. Express Yourself oh thanks! I really should have known this; it seems so obvious now. Well, at least I have the perfect idea of how to reuse this page.