Type Casting

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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;
Console.WriteLine($"The value of d+f is {tempVariable1}");
int tempVariable2 = a + d; // This line should give you an error.

Casting

Cast Operator

Create a new project, and then do the following.

  1. 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?

  2. Your IDE is suggesting that we use a “cast” to “force” C# to store the value of the variable floatVar into the variable intVar. To do so, replace the previous statement with the following:

    int intVar = (int)floatVar; // This statement will compile
  3. Using a Console.WriteLine statement, observe the value stored in intVar. Can you tell if the value stored in floatVar was rounded or truncated before being stored in the variable intVar? Conduct further experiments if needed to answer this question.

Implicit and Explicit Casting

  1. Look back at the warning given by the IDE. It uses the term “implicitly convert” before introducing the cast operator.

  2. While you needed a cast to convert a float to an int, do you need one to convert an int to a float? 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 valid float values, no explicit cast is needed!

  3. Do these cases need an explicit cast, or will an implicit conversion work? Try them in your IDE to check your answers!

  • double to int
  • int to double
  • float to double
  • double to float
  • int to decimal
  • decimal to float
  • float to decimal

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!