question about if-statements

[fabsy]

Im a newbie to ruby (hehe).
I have a question.
Is there any better way to do this? :

---------------
puts "Enter Username"
usr = gets
puts "Enter Password"
usr_pass = gets
User = "user"
Pass = "pass"

if usr > User
if usr_pass > Pass
puts "Correct user and pass"
else
puts "Correct user"
puts "Wrong pass"
end
else
if usr_pass > Pass
puts "Correct pass"
else
puts "Wrong pass"
end
puts "Wrong user"
end

------------------------This is the same but in VB---------
if usr = User and usr_pass = Pass then
print "correct user and password"
else
if usr = User and usr_pass <> Pass then
print "correct user and wrong password"
else
if usr <> User and usr_pass = Pass then
print "correct password and wrong user"
else
if usr <> User and usr_pass <> Pass then
print "wrong password and wrong user"
end if
end if
end if
end if
-----------------------------------------------------

-------And how do i do this in ruby? ------
If usr = User and usr_pass = Pass then
print "Correct User and Pass"
else
print "Wrong User or Pass"
endif

 

[Daniel Schierbeck]

Im a newbie to ruby (hehe).
I have a question.
Is there any better way to do this? :

---------------
puts "Enter Username"
usr = gets
puts "Enter Password"
usr_pass = gets
User = "user"
Pass = "pass"

if usr > User
if usr_pass > Pass
puts "Correct user and pass"
else
puts "Correct user"
puts "Wrong pass"
end
else
if usr_pass > Pass
puts "Correct pass"
else
puts "Wrong pass"
end
puts "Wrong user"
end

------------------------This is the same but in VB---------
if usr = User and usr_pass = Pass then
print "correct user and password"
else
if usr = User and usr_pass <> Pass then
print "correct user and wrong password"
else
if usr <> User and usr_pass = Pass then
print "correct password and wrong user"
else
if usr <> User and usr_pass <> Pass then
print "wrong password and wrong user"
end if
end if
end if
end if
-----------------------------------------------------

-------And how do i do this in ruby? ------
If usr = User and usr_pass = Pass then
print "Correct User and Pass"
else
print "Wrong User or Pass"
endif

Question 1:

print "enter username: "
username = gets.chomp # chomp removes the last newline

print "enter password: "
password = gets.chomp

# using constants may not be the best approach...
Username = "foo"
Password = "bar"

raise "incorrect username" unless username == Username
raise "incorrect password" unless password == Password

# the user is now authenticated

Question 2:

if username == Username and password == Password
# correct
else
# incorrect
end


Cheers,
Daniel

 

[Robert Klemme]

Im a newbie to ruby (hehe).
I have a question.
Is there any better way to do this? :

---------------
puts "Enter Username"
usr = gets
puts "Enter Password"
usr_pass = gets
User = "user"
Pass = "pass"

if usr > User
if usr_pass > Pass
puts "Correct user and pass"
else
puts "Correct user"
puts "Wrong pass"
end
else
if usr_pass > Pass
puts "Correct pass"
else
puts "Wrong pass"
end
puts "Wrong user"
end

puts "Enter Username"
usr = gets
puts "Enter Password"
usr_pass = gets

if usr > "user" && usr_pass > "pass"
puts "Login ok"
else
puts "Wrong credentials"
end

Note: typically you do not report whether the user name or the password
was invalid to give attackers as few information as possible.

Btw, why do you compare with greater than and a string?

Kind regards

robert

 

[fabsy]

Thanks!

Btw, why do you compare with greater than and a string?

I didn't know how to compare so I just guessed it would be greater
than.
How would you do if you where to do a program like mine? The way you
wrote or any other way?

 

[Matthew Smillie]

Thanks!

I didn't know how to compare so I just guessed it would be greater
than.
How would you do if you where to do a program like mine? The way you
wrote or any other way?

Well, you're testing for equality, so greater than wouldn't catch a
lot of cases. I'd suggest these:

if X != Y # X not equal to Y

unless X == Y # X equal to Y

You can pick the one that's more linguistically appealing to you,
though I have a hunch that 'if' is more popular than 'unless'.

matthew smillie.

 

[Daniel Schierbeck]

if X != Y # X not equal to Y

unless X == Y # X equal to Y

You can pick the one that's more linguistically appealing to you, though
I have a hunch that 'if' is more popular than 'unless'.

I only think that's because most other languages don't have `unless'


Cheers,
Daniel

 

[Matthew Smillie]

I only think that's because most other languages don't have
`unless'

That was my first intuition too, and I'm certain that's part of it,
but upon further reflection I think there's more to it as well. To
make an if and unless statement equivalent, you have to negate the
condition, leading to this basic schema:

(1) if X != Y <--> unless X == Y
(2) if X == Y <--> unless X != Y

Logically, everything's kosher, but linguistically there's a crucial
difference: the 'unless' form of (2) is a double negative. I'm sure
people are generally familiar with the admonition to avoid double
negatives in their writing, and it's for a good reason: people have a
hard time understanding multiple negations; to be fair, two is
usually not a problem, especially in familiar forms such as "not
unlike X", but in general it's not an easy task to not do
incorrectly. (see?)

So, if you assume that given the choice people won't use
linguistically-uncomfortable code, then there are two basic
comfortable 'if' forms, but only one comfortable 'unless' form.
Given the lovely, literary nature of Ruby code, this seems like a
reasonable assumption to make; so even if everyone were perfectly
familiar with 'unless' as a language construct, you'd still expect
'if' to outnumber 'unless'.

Not that I think this has much bearing on the language, just a neat
observation.

matthew smillie

[1] For an entertaining example, see the Language Log talking about a
Penny Arcade comic strip here:
http://itre.cis.upenn.edu/~myl/languagelog/archives/003437.html

 

[Daniel Schierbeck]

That was my first intuition too, and I'm certain that's part of it, but
upon further reflection I think there's more to it as well. To make an
if and unless statement equivalent, you have to negate the condition,
leading to this basic schema:

(1) if X != Y <--> unless X == Y
(2) if X == Y <--> unless X != Y

Logically, everything's kosher, but linguistically there's a crucial
difference: the 'unless' form of (2) is a double negative. I'm sure
people are generally familiar with the admonition to avoid double
negatives in their writing, and it's for a good reason: people have a
hard time understanding multiple negations; to be fair, two is usually
not a problem, especially in familiar forms such as "not unlike X", but
in general it's not an easy task to not do incorrectly. (see?)

So, if you assume that given the choice people won't use
linguistically-uncomfortable code, then there are two basic comfortable
'if' forms, but only one comfortable 'unless' form. Given the lovely,
literary nature of Ruby code, this seems like a reasonable assumption to
make; so even if everyone were perfectly familiar with 'unless' as a
language construct, you'd still expect 'if' to outnumber 'unless'.

Not that I think this has much bearing on the language, just a neat
observation.

Interesting thoughts (and cool example). I do however tend to use short,
one-liner conditional statements the most, in which I think `unless'
fits much nicer than `if not'.


Cheers,
Daniel