Implicit typing with var keyword in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the var keyword do in C#?

The var keyword lets the compiler automatically figure out the variable's type based on the value you assign to it. This is called implicit typing.

beginner

Can you use var without assigning a value right away?

No. When you use var, you must assign a value immediately so the compiler can determine the type.

beginner

What type will this variable have? <br>

var number = 10;

The variable number will be of type int because 10 is an integer.

intermediate

Is var the same as object type?

No. var is not a type itself. It tells the compiler to use the actual type of the assigned value. object is a specific type that can hold any data but is less specific.

intermediate

Why might you want to use var instead of explicitly writing the type?

Using var can make code cleaner and easier to read, especially when the type is obvious or very long to write. It also helps when the exact type is complex or anonymous.

What happens if you write var x; without assigning a value?

A x is null by default

B x becomes an object type

C Compiler error because type cannot be inferred

D x is dynamic type

You must assign a value when using var so the compiler can infer the type. Otherwise, it causes a compiler error.

What type does var name = "hello"; create?

A string

B object

C var

D char[]

The compiler infers the type string because "hello" is a string literal.

Which of these is a benefit of using var?

A It makes code shorter and easier to read

B It disables type checking

C It makes variables dynamic

D It allows variables to change type later

var helps by reducing clutter and making code cleaner, but type checking still happens at compile time.

Is this code valid? <br>var list = new List<int>();

A Yes, but list will be of type object

B Yes, the compiler infers the type List<int>

C No, you must specify the type explicitly

D No, var cannot be used with generic types

The compiler infers the type List<int> from the right side, so this is valid.

Which statement about var is false?

A <code>var</code> can only be used for local variables

B <code>var</code> requires immediate assignment

C <code>var</code> is resolved at compile time

D <code>var</code> variables can change type after assignment

Variables declared with var have a fixed type after assignment and cannot change type later.

Explain how the var keyword works in C# and when you should use it.

Think about how the compiler figures out the type and why it helps.

Describe the differences between var and object types in C#.

Consider how the compiler treats each and what happens at runtime.