Explicit declarations

Explicit declaration is where the type of the variables is specified during declaration.

int age = 23;
string name = "Lorem Ipsum";
double money = 123.45;

Console.WriteLine($"Type of age: {age.GetType()}");
Console.WriteLine($"Type of name: {name.GetType()}");
Console.WriteLine($"Type of money: {money.GetType()}");

Output:

Type of age: System.Int32
Type of name: System.String
Type of money: System.Double

Live-code example

Implicit declarations

C# compiler uses type inferencing to deduce the actual type of the variable declared with the keyword var. Note that (Docs, 2015)

1. var keyword can only be used for variables declared at method scope
2. an implicitly declared variable is strongly typed (just as if you had declared the type yourself), which is different from the dynamic type.

var age = 23;
var name = "Lorem Ipsum";
var money = 123.45;

Console.WriteLine($"Type of age: {age.GetType()}");
Console.WriteLine($"Type of name: {name.GetType()}");
Console.WriteLine($"Type of money: {money.GetType()}");

Output:

Type of age: System.Int32
Type of name: System.String
Type of money: System.Double

This is not allowed since age is statically-typed (as int)

// ERROR: Cannot implicitly convert type "string" to "int"
age = "123";

Implicit declaration is extremely useful for creating anonymous classes, which are used extensively in LINQ operation.

var anony = new {
  Name = "Lorem Ipsum",
  Age = 23,
  Money = 123.45
};
Console.WriteLine($"Type: {anony.GetType()}");
Console.WriteLine($"Name: {anony.Name} Age: {anony.Age} Money: {anony.Money}");

Output:

Type: <> f__AnonymousType0`3[System.String, System.Int32, System.Double]      <-- this will be different
Name: Lorem Ipsum Age: 23 Money: 123.45

References

1. Docs, M. (Ed.). (2015, July 20). var (C# Reference). Retrieved from https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/var