C# Data Types

C# Data Types

As we learned in the Variables chapter, a variable in C# must be defined with a specific data type. The data type tells the compiler what size the memory space needs to be and what kind of values can be stored in it.

Choosing the correct data type is crucial for memory efficiency and performance.

Data Type Categories

Data types in C# are primarily divided into two main categories: Value Types and Reference Types.

1. Value Types

Value types store the data directly in their own memory allocation. Examples include numbers, characters, and booleans.

2. Reference Types

Reference types do not store the actual data directly. Instead, they store a reference (or memory address) to where the data is located. The most common reference type is a string.

Using Floating Point Numbers (Float vs. Double)

When dealing with decimal numbers, double is the default type in C#. If you want to use a float, you must append an F or f to the end of the number.

using System;

class Program {
  static void Main() {
    float myFloatNum = 5.75F;
    double myDoubleNum = 19.99;
    Console.WriteLine(myFloatNum);
    Console.WriteLine(myDoubleNum);
  }
}

3. Implicit Typing (The var Keyword)

Instead of explicitly stating the data type, you can use the var keyword. The C# compiler will automatically figure out the data type based on the value assigned to it.

var myName = "Alice"; // Compiler knows this is a string
var myAge = 25;       // Compiler knows this is an int

Note: You must assign a value immediately when using var, otherwise the compiler will throw an error because it cannot guess the type.

4. Constant Variables

If you have a variable whose value should never change (like Pi or a database configuration URL), use the const keyword. This makes the variable "constant" and unchangeable.

const double PI = 3.14159;
// PI = 3.14; // ERROR: This will cause a compiler error!