Lecture "Programming languages", exercise 2 about 2020-2021 HOT 22 OPEN

@SarahTew @giorgiasampo

Indeed the comparisons with strings are alphabetical, but the one that comes first in a dictionary is lesser than the other. E.g.:

"this string" > "another string" is True since "t" (first character of the first string) is greater than "a"(first character of the second string)

from 2020-2021.

@giorgiasampo Thank you for your detailed explanation! I thought comparisons were purely just alphabetical by word (so whichever would come first in a dictionary was considered larger). Now I understand 👍

@essepuntato Thank you Professor Peroni. For anyone else that is confused about comparing strings I found this helpful explanation with a few simple exercises at the bottom to clear up the rules for comparing strings.

from 2020-2021.

False

Work:
True and not (True)
True and False
False

from 2020-2021.

The Boolean value is TRUE because:
-"spam" not in "spa span sparql" returns TRUE
-"egg"> "span" returns FALSE (I summed the values of the letters according to the alphabetical order so e=5, g=7, s=19, p=16, a=1, n=14 so egg=19 and span=50)
-not FALSE (result of previous operations) is TRUE
-TRUE and TRUE is TRUE

from 2020-2021.

"spam" not in "spa span sparql" -> T
not ("egg" > "span") -> not(F) -> T
"spam" not in "spa span sparql" and not ("egg" > "span") -> T

from 2020-2021.

“spam” not in “spa span sparql” and not (“egg”>”span)
-> “spam” not in “spa span sparql” and not False [first solve the part in the brackets]
-> True and True [second step solve the not operations]
-> True [finally solve the and operation]

from 2020-2021.

"spam" not in "spa span sparql" and not ("egg" > "span")
True and not ("egg" > "span")
True and not False
True and True
True

from 2020-2021.

"spam" not in "spa span sparql" and not ("egg" > "span")
True and not False
True and True then True

from 2020-2021.

The answer is True:
"spam" not in "spa span sparql" and not ("egg" > "span")
True and not False [("egg" > "span") is False because egg comes before (<) "span" in alphabet]
True and True
True

from 2020-2021.

The boolean value is True:

"spam" not in "spa span sparql" and not ("egg" > "span")
"spam" not in "spa span sparql" and not (False)
"spam" not in "spa span sparql" and True
True and True
True

from 2020-2021.

TRUE:
"spam" not in "spa span sparql" and not ("egg" > "span")
"spam" not in "spa span sparql" and not False
True and True
True

from 2020-2021.

The boolean value is TRUE.
First of all, we analyze the first condition about the two strings "spam" and "spa span sparql".
"Spam" NOT in "spa span sparql" = TRUE

So, we check the second one.

• NOT ("Egg"> "Span")
• NOT (FALSE) --> because the first letter of "Egg" comes before "S" in the alphabet, so it's not "greater than" the second one.
• TRUE

So, TRUE and TRUE= TRUE

from 2020-2021.

"spam" not in "spa span sparql" and not ("egg" > "span") => false because "s" is greater than "e" (I think I understand)
"spam" not in "spa span sparql" and not (False)
True and True
True

from 2020-2021.

"spam" not in "spa span sparql" and not ("egg">"span")?

True and not (False)
True and True = TRUE

from 2020-2021.

This expression returns the boolean value True

from 2020-2021.

"spam" not in "spa span sparql" and not ("egg" > "span").
"spam" not in "spa span "sparql" is TRUE. not("egg">"span") is TRUE ("egg" greater than "span" is false and with not TRUE)
TRUE and TRUE is TRUE
so TRUE

from 2020-2021.

The boolean value is True.

We solve the operation in () first. "egg" is not greater than "span" by alphabetical value, so the result is False. the first part is True ("spam" is not in the string). True and not False returns True.

from 2020-2021.

"spam" not in "spa span sparql" and not ("egg" > "span")
("spam" not in "spa span sparql") and not ( False )
(True) and (True)
True

from 2020-2021.

"spam" not in "spa span sparql" and not ("egg" > "span")

True and not False
True and True
True

from 2020-2021.

The Boolean value is True. Here is the procedure:

"spam" not in "spa span sparql" and not ("egg" > "span")

"spam" not in "spa span sparql" -> True

True and not ("egg" > "span")

("egg" > "span") -> False because "e" comes before "s"

True and not (False)

True and True

True`

from 2020-2021.

"spam" not in "spa span sparql" and not ("egg" > "span")
"spam" not in "spa span sparql" and not false
"spam" not in "spa span sparql" and true
true and true
true

from 2020-2021.

"spam" not in "spa span sparql" and not ("egg" > "span")
("egg" > "span") = F
"spam" not in "spa span sparql" = T
T and not (F)
not (F) = T
T and T
T

from 2020-2021.