loop

[jayshaw94]

When running this code below. If the person types in an answer that is within the limit (0,0.5,1,2)
I still get the error message. What am I doing wrong?
Thanks in advance!

var nojp:int
var op1:real
procedure OpeningDeductions
put "Enter the number of Jumbo post(s) required"
get nojp
put "Enter either 0, 0.5, 1, or 2"
loop
get op1
if op1 not = 0 or op1 not = 0.5 or op1 not = 1 or op1 not = 2 then
put "Error please enter the following 0, 0.5, 1, or 2"
put op1
end if
exit when op1 = 0 or op1 = 0.5 or op1 = 1 or op1 =2
end loop
end OpeningDeductions

[Tony]

Because testing for equality of real values is a bad idea
http://en.wikipedia.org/wiki/Floating_point#IEEE_754:_floating_point_in_modern_computers

Quote:

To a rough approximation, the bit representation of an IEEE binary floating-point number is proportional to its base 2 logarithm, with an average error of about 3%

[jayshaw94]

sorry Tony not sure what you mean. The program runs but I still get the error message if for instance i type in 5 I'll get the error message as I should. But if i type in one of the options available I get the error message but it continues onto the next line of code

[Insectoid]

Say someone enters 1. Now we check.

Does it equal 0? No.
Does it equal 0.5? No.
Does it equal 1? Yes!
The test fails, and we therefore get your error message.

'or' is obviously not working here. Try something else.

[Tony]

oh, that.

code:

op1 not = 0 or op1 not = 0.5 or op1 not = 1 or op1 not = 2

is guaranteed to always be true, for any value entered.

edit: damn you Insectoid!

[Insectoid]

I win again!

[jayshaw94]

thanks guys what other syntax would i be able to use?

[Tony]

OR could work, if you ask the right question. Keep in mind that this is a mathematical OR. In speech "or" often means "xor" instead, thus the confusion.

Some references
or
xor
and
not

[jayshaw94]

Thank you Tony I'll look into it some more
thanks again