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If you declare a variable within a method, it's only accessible within that method. But trust us, that's a good thing!
- Variable declared within a method is accessible only within that method
- Can declare multiple variables with same name in different scopes
using System;
class Program
{
static void MyMethod()
{
// This "total" variable is completely
// separate from the "total" variable in
// the Main method!
int total = 0;
total += 1;
Console.WriteLine("total in MyMethod:");
Console.WriteLine(total);
}
static void Main(string[] args)
{
int total = 0;
total += 10;
MyMethod();
Console.WriteLine("total in Main:");
Console.WriteLine(total);
}
}
total in MyMethod:
1
total in Main:
10
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A variable that's declared within a method
is accessible only within that method.
0:00
Let me show you what I mean.
0:04
So here, we have a program that, within
the main method, declares a variable,
0:06
total, and then adds 10 to its value.
0:10
And you can see down in the console
that it prints that value, 10.
0:13
But what if we were to add another method
and try to access total within it?
0:16
So let's add one called
static void MyMethod.
0:20
And here, in the method body, I'm going to
attempt print the value of total again.
0:25
Console dot WriteLine, total in my method.
0:29
Console dot WriteLine total.
0:32
Let me save that, and go down to
the console and try running this.
0:34
Up arrow to bring up dotnet run again,
Enter to run it.
0:40
I get a compile error.
0:43
The name total does not exist
in the current context.
0:45
And it says it's on line 8,
which is within my method.
0:48
So here's the problem.
0:53
We declared the total variable down here,
but
0:54
no total variable exists up
here within the MyMethod body.
0:56
This is what's known as variable scoping.
1:00
A variable scope is the portion of
the program code that that variable is
1:03
visible within.
1:08
So since we declare this total
variable within the Main method,
1:09
it's visible only within Main.
1:13
When we try to access it up here,
we get a compile error.
1:16
If we want to access a variable
name total up here in MyMethod,
1:19
we're going to have to declare a separate
total variable up here in MyMethod.
1:23
Now, even though this variable is named
total and this variable is name total,
1:31
these two entirely separate variables.
1:35
Let me try placing a call to
MyMethod down here within Main.
1:38
And let's try running it again.
1:46
And you can see that, here, we declare
the variable total, set it to 0.
1:50
Then we add 10 to it so
that total is set to 10.
1:56
Then, we call MyMethod.
1:59
Up here, in MyMethod, we declare
an entirely separate variable that is also
2:03
named total, and we set its value to 0.
2:06
Then, we print the value of
total down here on line 9.
2:09
And you'll notice that it says here
in the output, total in MyMethod, 0.
2:13
At that point, MyMethod finishes, and
it goes back to the Main method where we
2:19
print total in Main, and then print the
total variable as it exists within main.
2:25
And you'll notice that the value
of total in main is 10.
2:31
Even though we set total
back to 0 up here,
2:34
that's a totally separate total variable.
2:36
We set this total variable to 10 up here,
and
2:39
therefore that's what gets
printed down here, 10.
2:42
And this variable scoping
is actually a good thing.
2:47
When your program gets really big, and
you want to declare a variable name total,
2:50
you don't wanna have to worry about
whether there's some variable name
2:54
total elsewhere in your program.
2:57
If it weren't for variable scoping,
you would have to worry about that.
2:59
But because the total variable within
MyMethod is totally separate from
3:03
the total variable within Main, we can go
ahead and do whatever operations we want
3:07
on one total variable without worrying
about how it will affect the other.
3:12
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