Testing for a Sentinel Value

You might have made another choice for the blank. But the program has to work for any number that the user might have entered. For that, only not equal will work.

' Add up numbers that the user enters.
' When the user enters 0, print the sum and end the program.
'
LET SUM = 0
'
PRINT "Enter a number"       
INPUT NUMBER                 
'
DO WHILE NUMBER <> 0
  LET SUM = SUM + NUMBER   
  PRINT "Enter a number. (Type 0 to stop)"       
  INPUT NUMBER                 
LOOP
'
PRINT "The sum is", SUM
END

Now say that the program has been running for a while. The user has been entering numbers to be added. The monitor might look something like:

Enter a number
? 4
Enter a number. (Type 0 to stop)
? 2
Enter a number. (Type 0 to stop)
? 3
Enter a number. (Type 0 to stop)
? 

Neither the 2 nor the 3 will cause the program to stop.