Ruby Programming Tutorial - 20 - Constants Video Lecture | Introduction to Coding with Ruby - Back-End Programming

what is going on guys welcome to your
20th real beat sorrow and in this lesson
I want to talk to you guys about
something called constants now constants
are similar to variables but whenever I
try to explain these to people I say
this constants are variables whose
values don't change what the heck does
that mean
well say that we created a variable
called tuna and we set it equal to 18
then we can go ahead and use that
variable in our program print it out on
the screen if we want and it prints out
18 but then later on we're like you know
what actually I wanted that tuna
variable equal to 34 so Ruby says okay
no problem I'll just change the value of
it and then we can use it from now on
and the new value is 34 so basically a
variable is a placeholder and we could
change the value of it whenever we want
however there are often times whenever
you're building a computer program where
you want something to be a placeholder
of a value but you don't want the value
to change for example whenever you're
making the variable PI you want to set
this equal to 3.14159 and you want to
set this forever
the value of pi never changes and
basically you don't want the user to
accidentally change your variable you
don't want any other programs to change
your variable so you don't want to treat
this as a normal variable so what we
want to do is we want to store this
value right here in PI but we don't want
it to be able to change anytime you want
to write a variable like this we want to
create a constant now whenever you're
creating a constant this is how you do
it it's very easy instead of just naming
a variable anything you need to start it
out with a capital letter so if you
create a variable like this that starts
with a capital letter you're actually
creating a constant now let's go ahead
and set Bucky equal to 25 because that's
my age and it looks like we're just
creating a variable but we are indeed
creating a constant how can we prove
this well let's just go ahead and try to
run this baby
so print Bucky okay it runs fine
but now let's go ahead and try to change
the value of Bucky we say okay actually
Bucky
25 he's actually only 12 years old so
now we're just gonna go ahead and change
the value no big deal
whoa whoa whoa what the heck is this
well whenever we tried to change it
Ruby's pretty much gonna yell at us it
will let us change the value but we're
gonna get a warning says hey dude you
already initialized the constant Bucky
which pretty much means you already
created a constant Bucky and you weren't
supposed to change the value you
promised me you wouldn't change the
value so why the heck did you change the
value and it just gives us a hard time
about it so that's the difference
between variables and constants Wow and
I want to mention this because a lot of
people who learn other programming
languages are gonna get confused about
this because it's different in Ruby than
other ones whenever you create a
constant in basically any other computer
language and you try to change the value
then your computer program is basically
gonna shut down and give you a bunch of
error messages and it will stop running
however in Ruby what happens is it does
indeed changed value so the new value of
Bucky is indeed 12 it just gives you a
little warning so that's a key thing
about Ruby where you have to remember
and that's one of the thing that
separates it from other programming
languages so now whenever we try to
print Bucky out on the screen we can see
that the new value is indeed 12 in our
computer program didn't get destroyed or
anything it just gives us a hard time
about it and warns us whenever we change
the consonant so again guys remember
whenever you have a variable that's
value is going to change start it out
with a lowercase letter
and whenever you want to make constants
such as pi in a lot of math numbers that
are like constants of course start those
out with capital letters so anyways
thank you guys for watching don't forget
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next video