Implicit typing with var keyword in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this C# code using var?

Consider the following code snippet. What will be printed to the console?

C Sharp (C#)

var x = 10;
var y = 3.5;
var z = x + y;
Console.WriteLine(z);

A 13.5

B 13

C Error: Cannot add int and double implicitly

D 10 3.5

💡 Hint

Remember that var lets the compiler infer the type and that adding int and double results in a double.

The variable z is inferred as double because x (int) and y (double) are added, resulting in a double value 13.5.

❓ Predict Output

intermediate

What type does var infer here?

What is the type of variable 'data' in this code?

C Sharp (C#)

var data = new List<string> { "apple", "banana" };

A List<string>

B object

C IEnumerable<int>

D string[]

💡 Hint

Look at the right side: new List creates a list of strings.

The compiler infers 'data' as List because the right side explicitly creates a List.

🔧 Debug

advanced

Why does this code cause a compilation error?

Examine the code below. Why does it fail to compile?

C Sharp (C#)

var x;
x = 5;

A var cannot be assigned an int value

B Missing semicolon after var

C var requires initialization at declaration

D x is a reserved keyword

💡 Hint

var needs to know the type immediately from the assigned value.

In C#, var variables must be initialized when declared so the compiler can infer the type. Declaring 'var x;' without initialization causes an error.

❓ Predict Output

advanced

What is the output of this code with var and anonymous types?

What will this program print?

C Sharp (C#)

var person = new { Name = "Anna", Age = 30 };
Console.WriteLine($"{person.Name} is {person.Age} years old.");

A Name Age

B Anna is 30 years old.

C Anna30

D Error: Anonymous types cannot be used with var

💡 Hint

Anonymous types can be assigned to var and their properties accessed.

The anonymous type is assigned to 'person' and its properties Name and Age are accessed correctly, printing the formatted string.

🧠 Conceptual

expert

Which statement about var is true in C#?

Choose the correct statement about the var keyword in C#.

A var is a keyword to declare variables of type object

B var can be used without initialization if the type is declared later

C var variables are dynamically typed and can change type at runtime

D var variables must be initialized at declaration and their type is fixed at compile time

💡 Hint

Think about how var works with type inference and static typing.

In C#, var is a compile-time feature where the compiler infers the type from the initialization expression. The type is fixed and cannot change at runtime.