Modern C# and .NET Tutorial: Cross-Platform Basics/

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Casting and Converting Between Types

Casting and Converting Between Types

Learn about casting for implicit and explicit conversions, rounding rules, and using System.Convert, parsing from strings to other data types.

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We will often need to convert the values of variables between different types. For example, data input is usually entered as text at the console, initially stored in a string type variable. Still, depending on how it should be stored and processed, it must be converted into a date/time, number, or other data type. Sometimes, we must convert between number types, like an integer and a floating point, before calculating.

Casting

Converting, also known as casting, has two varieties: implicit and explicit.

  • Implicit casting: Happens automatically and is safe, meaning we will not lose any information.

  • Explicit casting: This must be performed manually because it may lose information, such as a number's precision. By explicitly casting, we tell the C# compiler we understand and accept the risk.

Casting numbers implicitly and explicitly

Implicitly casting an int variable into a double variable is safe because no information can be lost, as the following shows:

Step 1: Use your preferred coding tool to add a new "Console App or console project" named CastingConverting to the Chapter03 workspace/solution.

  • In Visual Studio Code, select CastingConverting as the active OmniSharp project.

Step 2: In the Program.cs, delete the existing statements and then type statements to declare and assign an int variable and a double variable, and then implicitly cast the integer’s value when assigning it to the double variable, as shown in the following code:

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int a = 10;
double b = a; // an int can be safely cast into a double
WriteLine(b);

Step 3: Type statements to declare and assign a double variable and an int variable, and then implicitly cast the double value when assigning it to the int variable, as shown in the following code:

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double c = 9.8;
int d = c;
WriteLine(d); // d is 9 losing the .8 part

Step 4: Run the code and note the error message, as shown in the following output:

Error: (6,9): error CS0266: Cannot implicitly convert type 'double' to
'int'. An explicit conversion exists (are you missing a cast?)

This error message will also appear in the Visual Studio error list or Visual Studio Code problems window. We cannot implicitly cast a double variable into an int variable because it is potentially unsafe and could lose data, like the value after the decimal point. We must explicitly cast a double variable into an int variable using a pair of round brackets around the type into which we want to cast the double type.

The pair of round brackets is the cast operator. Even then, we must beware that the part after the decimal point will be trimmed off without warning because we have chosen to perform an explicit cast and understand the consequences.

Step 5: Modify the assignment statement for the d variable, as shown in the following code:

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int d = (int)c;
WriteLine(d); // d is 9 losing the .8 part

Step 6: Run the code to view the results, as shown in the following output:

10
9

When converting values between larger and smaller integers, we must perform a similar operation. Again, beware that we might lose information because any value too big will have its bits copied and interpreted in ways we might not expect.

Step 7: Enter statements to declare and assign a long 64-bit variable to an int 32-bit variable, both using a small value that will ...