Syntax error on simple If Else

Question

I get an error at the 'Else' on a TI-84 Plus. I can't figure out why this doesn't work.

I'm writing a GCD program just as an exercise in programming a TI calculator. It's recursive (or as recursive as TI-BASIC gets).

If B=0
Disp A
Else
C->B
B->remainder(A,B)
A->B
prgmGCD2

Answer 1

TI-Basic is often rather picky about the syntax of if statements.

There are three general formats for an If statement.

Single Statement If

:If <boolean>
:<expression>

Note that <expression> consists of exactly one line of code.

Multi Statement If

:If <boolean>
:Then
:<expresion>
:<expresion>
:End 

As opposed to the first option, this option can contain any number of lines of code after the If.

If Else

:If <boolean>
:Then
:<expresion>
:<expresion>
:Else
:<expresion>
:<expresion>
:End

As with the previous option, any number of statements can be put after the If and after the Else.

---

You are obviously trying to use an if else statement. The correct syntax for this is:

:If B
:Then
:C->B
:B->remainder(A,B)
:A->B
:prgmGCD2
:Else
:Disp A
:End