C# DataType MCQs

Question 31: What will the output of the following program?

public static void Main(string[] args)
{
	object o1 = "csharp";  
    char[] arr = {'c','s','h','a','r','p'};  
    object o2 = new string(arr);   

	Console.Write(o1 == o2);
	Console.Write(o1.Equals(o2));
}

Answer: B

The == operator compares the reference of the operand, and the Equals() method compares the content. Since o1 and o2 are different string objects, so == returns false, whereas the content of o1 and o2 are the same, so the Equals() method returns true.

Always use the Equals() method to compare reference type variables; otherwise, you may get the wrong result.

Question 32: What will be the output of the following code? 

int? x = null;
int y = x ?? -1;

Console.Write(y);

Answer: C

The int? is a nullable type, so null can be assigned to it. The ?? operator checks for null, x??-1 indicates that if x is null, then -1. So the output would be -1.

Question 33: What will be the output of the following program?

object obj = "hello";
Type t1 = typeof(obj); 
Type t2 = obj.GetType();  

Console.Write(t1 == t2);

Answer: A

The typeof operator can be used with the type or generic type known at compile-time. The typeof(obj) will give a compile-time error because obj is a variable, not a type. You can use the typeof with type, e.g., typeof(int). The GetType() is called on an object at runtime. In both cases, the return type will be an object of the System.Type.

Question 34: What will be the output of the following program?

static void Main(string[] args)
{
    object obj = "hello";
    Type t1 = typeof(object); 
    Type t2 = obj.GetType();  

    Console.Write(t1 == t2);
}

Answer: B

The typeof(object) method will return object and the obj.GetType() returns “String”. Typeof() returns type name known at compile-time and the GetType() method returns type name at runtime.

Question 35: What will be the output of the following program?

int i = null;
Console.WriteLine(i);

Answer: C

You cannot assign null to the value type variables. Thus, trying to assign null to int will give a compile-time error. Use the Nullable<int> instead. Visit C# Nullable Types for more information.

Question 36: What will be the output of the following program?

static void Main(string[] args)
{
    int? i = null;
    int j = 10;

    if (i < j)
        Console.WriteLine("i < j");
    else if( i > 10)
        Console.WriteLine("i > j");
    else if( i == 10)
        Console.WriteLine("i == j");
    else
        Console.WriteLine("Could not compare");
}

Answer: D

Null is considered to be less than any value. So comparison operators won't work against null. Use the Nullable helper class to compare values.

Learn C# Nullable Types.

Question 37: What will be the output of the following program?

static void Main(string[] args)
{
    int? i = null;
    int j = 10;

    if (Nullable.Compare(i, j) < 0)
        Console.WriteLine("i < j");
    else if (Nullable.Compare(i, j) > 0)
        Console.WriteLine("i > j");
    else
        Console.WriteLine("i = j");
}

Answer: A

A null value is considered to be less than any value. So comparison operators won't work against null. Use the Nullable helper class to compare values.

Learn C# Nullable Types.

Question 38: Which of the following statements is TRUE?

Answer: D

Question 39: What will be the output of the following program?

static void Main()
{
    object[] arr = new String[10];
    arr[0] = 100;
    
    Console.Write(arr[0]);
}

Answer: D

Covariance for arrays enables implicit conversion of an array of a more derived type to an array of a less derived type. But this operation is not type-safe, and so the above code will throw a runtime exception.

Learn C# Covariance and contravariance.

Question 40: What will be the output of the following program?

static void Main()
{
    var emp = new
    {
        Id = 1,
        Name = "Steve",
        isActive = true
    };

    emp.Name = "James";
    Console.Write(emp.Name);
}

Answer: C

Here, emp is an anonymous type. Properties of anonymous types are read-only, and so it will give a compile-time error. Learn C# anonymous types.