83Plus:Basic:If - Revision history

Aquanight at 19:48, 19 July 2005

2005-07-19T19:48:09Z

AndyJ: /* Examples */ + or choose it from the catalog

2005-07-19T18:50:42Z

‎Examples: + or choose it from the catalog

AndyJ: screw it, gonna use ( ) instead of [ ] for optional

2005-07-19T18:49:30Z

screw it, gonna use ( ) instead of [ ] for optional

AndyJ: growl

2005-07-19T18:48:48Z

growl

AndyJ: ok this is going to take experimenting

2005-07-19T18:48:25Z

ok this is going to take experimenting

AndyJ: changed category sort key

2005-07-19T18:47:15Z

changed category sort key

AndyJ: /* Synopsis */ + If...Then...Else...End

2005-07-19T18:44:46Z

‎Synopsis: + If...Then...Else...End

Aquanight at 15:33, 19 July 2005

2005-07-19T15:33:44Z

New page

[[Category:83Plus:Basic:Conditionals|If]]
== Synopsis ==
'''Token Size:''' 1 byte

'''Syntax:'''
If ''condition''
''command''

If ''condition''
Then
''commands''
End

If the specified condition evaluates to a real number equal to 0, ''command'' is skipped. If the condition evalutes to a real number not equal to 0, ''command'' is executed. ''command'' may be a single command, or it can be the command '''Then''', in which case all commands until a corresponding '''End''' token are part of ''command''.

== Comments ==
Repeated use of a Goto statement within an If:Then statement will cause an increase in memory allocation, leading to program slowdowns and eventually a MEMORY error. For example, the following code will eventually cause an error:

<nowiki>0->X ;-> == STO operator
Lbl 0
If 1
Then
X+1->X
Disp X
Goto 0
End</nowiki>

If you must use a Goto within an If:Then statement, it is possible to trick the 83+ into thinking the block ended by jumping to an otherwise unused label that uses an End statement followed by a jump to the proper label. For example, the above program could be rewritten like so:

<nowiki>0->X
Lbl 0
If 1
Then
X+1->X
Disp X
Goto 2
End
Return

Lbl 2
End
Goto 0</nowiki>

This would avoid the problem by causing the 83+ to terminate the If:Then block prior to jumping.

Since TI-BASIC has no equivalent of what real BASIC calls Select Case, multiple Ifs must be used in cases where a variable needs to be checked against multiple values.

== Examples ==

A particular example is a keyloop.
Assuming a keycode was stored in K, a sequence of If statements would compare K to the corresponding integer key value.

If K=21
Disp "2ND"
If K=31
Disp "ALPHA"
If K=22
Disp "MODE"
If K=32
Disp "X,T,''θ'',''n''" ;''θ'' == Alpha+0. To get the italic n, switch to Seq mode and press the X,T,''θ'',''n'' key.

@@ Line 65: / Line 65: @@
   Disp "MODE"
   If K=32
-  Disp "X,T,''&theta;'',''n''" ;''&theta;'' == Alpha+0. To get the italic n, switch to Seq mode and press the X,T,''&theta;'',''n'' key.
+  Disp "X,T,''&theta;'',''n''" ;''&theta;'' == Alpha+0. To get the italic n, switch to Seq mode and press the X,T,''&theta;'',''n'' key or choose it from the Catalog.

@@ Line 1: / Line 1: @@
-[[Category:83Plus:Basic:Conditionals|If[...Then[...Else]...End<nowiki>]</nowiki>]]
+[[Category:83Plus:Basic:Conditionals|If(...Then(...Else)...End)]]
 == Synopsis ==
 '''Token Size:''' 1 byte

@@ Line 1: / Line 1: @@
-[[Category:83Plus:Basic:Conditionals|If[...Then[...Else]...End]]]
+[[Category:83Plus:Basic:Conditionals|If[...Then[...Else]...End<nowiki>]</nowiki>]]
 == Synopsis ==
 '''Token Size:''' 1 byte

@@ Line 1: / Line 1: @@
-[[Category:83Plus:Basic:Conditionals|If<nowiki>[...Then[...Else]...End]</nowiki>]]
+[[Category:83Plus:Basic:Conditionals|If[...Then[...Else]...End]]]
 == Synopsis ==
 '''Token Size:''' 1 byte

@@ Line 16: / Line 16: @@
   ''commands''
   Else
-  ''commands''
+  ''commands-else''
   End
-If the specified condition evaluates to a real number equal to 0, ''command'' is skipped. If the condition evalutes to a real number not equal to 0, ''command'' is executed. ''command'' may be a single command, or it can be the command '''Then''', in which case all commands until a corresponding '''End''' token are part of ''command''. When using '''Else''', one must also use '''Then''' and '''End'''.
+In the first from, ''command'' is executed if and only ''condition'' evaluates to anything other than 0. In the second form and third form, ''commands'' is also executed if and only if ''condition'' is not zero. In the third form, if ''condition'' is zero, ''commands-else'' is executed.
 == Comments ==