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Here we have some code that
assigns the integer 12 to

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a variable named wholeNumber.

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And the fractionalNumber, 12.34,
to a variable named fractionalNumber.

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That decimal point within the numbers
is important because it decides which

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of C sharp's two most common numeric
types the number will be treated as.

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The wholeNumber automatically gets
assigned the type of Int32, and

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the number with the decimal
point gets a type of Double.

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As we saw in the previous video,
even a number that's technically and

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integer will be treated as a double,
if you include a decimal point.

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Let's change the assignment to
wholeNumber from 12 to 12.0.

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It's still, technically,
the same number, but

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the decimal point changes
its default type.

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You can see that the type for
wholeNumber is now also Double.

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Remember that the var keyword
implicitly sets the type of a variable

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based on the value you
initially set it to.

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We can also explicitly set
the type of our variables.

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Let me set wholeNumber's type to int, and

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fractionalNumber's type to double,
save that and run it.

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But this gives us an error
when assigning to wholeNumber.

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Cannot implicitly convert type 'double'
to 'int', what does that mean?

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Well, this really doesn't seem to
matter much when assigning 12.0 to

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an integer variable.

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But what if we were trying
to assign 12.5 or 3.14, or

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some other number with a fractional part?

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For an integer variable
to hold the double value,

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we have to convert it to an integer.

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But what do we do with
the fractional part, the 0.75?

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Does it just not matter, can we drop it?

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That seems unlikely, you wouldn't want
the fractional dollars dropped from

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your bank account, for example.

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To protect you from issues like this, C
sharp won't let you assign a double value

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to a int variable without
converting it first.

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A conversion shows the compiler that
you know this is a double value, but

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you definitely want to
convert it to an int.

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It shows you are certain there’s either
no fractional portion to the number, or

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that losing the fractional
portion won’t cause any problems.

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You do a conversion by placing parentheses
before the value you want to convert,

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containing the type you want
to convert the value to.

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So in this case, we want to convert
this double value, 12.75, to an integer.

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Let's try saving this and
see if it runs now.

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Everything works again, this value,
12.75, which is the double by default,

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has been converted to an int.

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Conversions only work with numeric types.

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For example, you can't convert
from a string to an int, and

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you can't convert from an int to a string.

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If I try, I get compile errors.

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There are often other ways to convert
from one non-numeric type to another, but

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those are provided by libraries.

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Conversions, on the other hand,
are provided by the language itself.

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We'll see how to convert from a string
to a numeric type in an upcoming video.

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Casting is an explicit conversion, it's
required when making a conversion from

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a more precise numeric type to a less
precise one because data might be lost.

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Converting from a floating-point number to
an integer loses all the decimal places,

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for example, so
it requires an explicit cast.

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But when you're converting from a less
precise numeric tied to a more precise

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one, there's no risk of data loss.

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Because, the most precise,

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numeric type will always be able to hold
the full value from the less precise one.

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For example, when converting from
an integer to a floating-point number,

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you can just add a 0.0 onto the end.

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It consumes more memory to store it now,
but it's still the same value.

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When converting from a less precise
numeric type to a more precise one,

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C sharp will do an implicit cast.

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An implicit cast is a conversion between
numeric types that happens automatically

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without the need to
specify that it should.

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For example, suppose I wanted to change
the initial value of fractional number

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from 12.34 to just 12.

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There's no need to write 12.0,

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I can just get rid of the decimal
point and all the decimal places.

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It still works and the resulting
value still has a type of double

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because I declared fractional
number with a double type.

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C sharp did an implicit conversion
from the less precise int type

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to the more precise double type.