Type Casting
May 21, 2022 (04:25:12 PM)
Numerical Datatypes
For this part, it is recommended to have the datatypes cheatsheet readily available. Note that it contains numerous references at its end. You are encouraged to open those links, if you have not already, to have a look at the official documentation, which should not scare you.
Literals and Variables
This part should be first carried out without using an IDE, but with pen and paper.
Assume we have the following statements:
int a = 21, b = 4;
float f = 2.5000000f;
double d = -1.3;
decimal m = 2.5m;
Answer the following:
- How many variables are declared?
- What are their datatypes?
- What are their values?
- What are their names?
Operations
- Consider the following expressions, which use the variables we have declared above. For each of them, tell if they are legal and if so, give the result and its corresponding datatype. The first two are given as examples:
Operation | Legal? | Result | Datatype |
---|---|---|---|
a + d |
Yes | 19.7 | double |
m + f |
No | N/A | N/A |
a / b |
|||
b * f |
|||
d + f |
|||
d + b |
|||
a + m |
|||
f / m |
|||
d * m |
You can check your answers using an IDE: create a new project, copy the variable declarations and assignments, and write your own statements to perform the calculations in the Main
method. For instance, if you want to check that the result of a + d
is of type double
, write something like:
double tempVariable1 = a + d;
.WriteLine($"The value of d+f is {tempVariable1}");
Consoleint tempVariable2 = a + d; // This line should give you an error.
Casting
Cast Operator
Create a new project, and then do the following.
Add in your program the following:
float floatVar = 4.3f; int intVar = floatVar; // This statement will give you an error
You will get an error that reads
Cannot implicitly convert type 'float' to 'int'. An explicit conversion exists (are you missing a cast?)
Can you explain it?
Your IDE is suggesting that we use a “cast” to “force” C# to store the value of the variable
floatVar
into the variableintVar
. To do so, replace the previous statement with the following:int intVar = (int)floatVar; // This statement will compile
Using a
Console.WriteLine
statement, observe the value stored inintVar
. Can you tell if the value stored infloatVar
was rounded or truncated before being stored in the variableintVar
? Conduct further experiments if needed to answer this question.
Implicit and Explicit Casting
Look back at the warning given by the IDE. It uses the term “implicitly convert” before introducing the cast operator.
While you needed a cast to convert a
float
to anint
, do you need one to convert anint
to afloat
? Try the following:int intVar = 21; float floatVar = intVar; // Does this need a cast?
Generally, you need an explicit cast if an implicit conversion would lead to data loss. Since all possible
int
values are also validfloat
values, no explicit cast is needed!Do these cases need an explicit cast, or will an implicit conversion work? Try them in your IDE to check your answers!
double
toint
int
todouble
float
todouble
double
tofloat
int
todecimal
decimal
tofloat
float
todecimal
That last result may have been surprising. While decimal
is higher precision than float
and double
, it requires an explicit cast from either of those types, as you want to “force” imprecise data into a datatype that is supposedly extremely precise. Think about measuring wood with an inaccurate tape measurer and then cutting it with laser precision: that is what storing a float
into a decimal
is!