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The function you have seen in
the previous lesson is very simple,

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and it will do the same
thing every time you call it,

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which is just to print hello, and
then, well, let's just remove that.

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So it's just going to print hello
every time you call the function.

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Now you can add parameters to a function.

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A parameter is simply
a variable you are going

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to pass to the function
when you call it.

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And then inside the function, you can
use this variable to do anything you want.

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And let's see this with an example.
Let's continue with our say hello function.

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Let's say we want now
to say hello with the name.

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So we want to pass a name to the
function to say hello to that name.

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I'm going to add a
parameter here, user name.

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So this is going to be a
variable inside the function.

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And now I can use the variable in the
function, for example, hello plus user name.

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So as you can see, I
can reuse the parameter.

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So this is a variable.
This is the same thing.

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I can reuse the parameter
I got in the function directly

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inside the function, inside
the execution of the function.

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Now if I run this, I'm
going to have an error.

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Why is that? Because here I
am calling the function say hello,

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and you can see missing one
required positional argument username.

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Actually, let's remove this.
Let's just call it once.

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Okay, so say hello. The
thing now is that there

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is no function say hello
with zero parameter.

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There is one function say
hello with one parameter.

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So I need to give it a parameter. And
here I'm going to give it a username, Bob.

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So say hello, Bob. And then Bob is
going to be passed as a parameter here,

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and we can use it in the function.
Let's run that.

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Hello, Bob.
Okay, so that is very convenient.

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Now what I can do is I can do say hello.

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So I can use the autocompletion
here, and let's say John.

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And as you can see,
hello, Bob, and hello, John.

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So we have the same exact
same code for the function,

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but with the parameters,
we can make it more dynamic.

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Okay, depending on what
we pass in the parameter,

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the execution of the function
would be different here.

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And of course, you can add as
many parameters as you want.

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Let's say you want also the user age.

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So I can do hello username, and then plus
comma, you are, and then plus user age.

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So now those two
functions are, those two

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calls to the functions
are not correct anymore,

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because now we need
to pass two parameters.

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And the order is very important.

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You need to pass the first user
name and then the user age.

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So Bob, and let's say 45,
and John, and let's say 42.

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I'm going to run the main, and
you can see we have an error.

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Okay, and this is why this is a cast error.

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You can only concatenate
string with string and not integer.

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So here we have a user age that
we just concatenate with this string.

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The problem is that
we pass an integer here.

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Okay, that's quite normal
because that's a user age.

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So what do we need to
do in the print function?

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We need to cast this integer into a string.

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So we need to call the str here.

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We need to cast to str
inside this username.

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We didn't have the error
before because we pass a string.

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So this we know this
is going to be a string.

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This might be an integer, so
we are going to cast it to string.

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Now I run it, and it's going to work.

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Hello, Bob, you are 45.

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Hello, John, you are 42.

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Okay, so you can make this function
much more complex with many lines of code,

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and then you can call it
as many times as you want.

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And with different
parameters, you are going

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to have different
code executions, okay?

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But you just need to write
the function once, and that's it.

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So to recap, with parameters, you
can make your functions more dynamic.

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With just one block of code in a function,
you can repeat a set of instructions with

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different values any
number of times you want.