C# DataType MCQs

Question 21: What will be the output of the following program?

public static void Main(string[] args)
{
	object o = "Bill";
		
	Console.WriteLine(o.GetType());
}

Answer: B

The type of object depends on the assigned value's type. If it is a string, then it will be of string type, and if it is int, then it will be of int type. Here string is assigned to an object o, so the type will be of string type.

Question 22: What will be the output of the following program?

public static void Main(string[] args)
{
	object o = "Bill";
	Change(o);
}
static void Change(object obj)
{ 
	Console.Write("object");
}
	
static void Change(string str)
{ 
	Console.Write("string");
}

Answer: A.

Above, the method gets called based on the type of variable passed. The type of o is declared as object, so it will call the Change(Object obj) method whose parameter type is an object. If you pass the string type variable, then it will call the Change(string str) method. Note it calls an overloaded method based on the type of a variable declared, not on the type of a value assigned.

Question 23: What will be the output of the following program?

public static void Main(string[] args)
{
	int i=10;
	float f = 34.412F;
	display(i);
	display(f);
}

static void display(float f){
	Console.Write(f + " ");
}

Answer: C.

An int is converted to float implicitly. However, the float cannot be converted to int implicitly. Above, when an int is passed in the display(float f) method, it gets converted into float implicitly.

Learn C# number types.

Question 24: What will be the output of the following program?

public static void Main(string[] args)
{
	int i=10;
	float f = 34.412F;
	display(i);
	display(f);
}

static void display(int i){
	Console.Write(i + " ");
}

Answer: A.

The float value cannot be converted implicitly, so the above program will give a compile-time error because it cannot find the display() method with float parameter for display(f). You must convert float to int explicitly.

float x = 10.5F;
int y = (int)x;
Console.WriteLine(y);

Question 25: Which of the following convert a string to an int?

Answer: A, B, C, D

In C#, string to int can be converted explicitly, using Convert.ToInt32() method, using int.Parse() method, and using int.TryParse() method.

Question 26: What will be the output of the following program?

public class Program
{
	public static void Main(string[] args)
 	{
		for(int i=0;i<4;i++)
			Printer.Print(i);
	}
}

public class Printer
{
	public static void Print(object o)
    {
        Console.Write(o);
    }
}

Answer: C

This is the example of boxing, which converts a value type to a reference type, e.g., int to object.

You can pass an int argument for the object type parameter because an int is an alias of the Int32 class derived from the Object class.

Question 27: What will be the output of the following program?

object o  = "Hello"
string s1 = o;

Console.Write(s1);

Answer: C

You cannot convert an object to a string implicitly. You must convert it explicitly, e.g., string s1 = (string) o;

Question 28: What will be the output of the following program?

static void Main()
{
    object obj = "Hello";

    Console.Write(obj is string);
}

Answer: C

The is keyword evaluates type compatibility at runtime. It also determines whether an object or the result of an expression can be converted to the specified type or not. The is statement returns true if the specified expression is non-null and the returned value can be converted to the specified type; otherwise, it returns false. Learn C# is keyword.

Question 29: String is _______ .

Answer: B

C# String is the immutable reference data type, which means once a string is created and stored in a memory, you cannot modify it. If you edit it, then CLR treats it as a new string at the new memory location. The StringBuilder is mutable. So, use it if your program needs to modify/concatenates strings multiple times to gain faster performance and optimum memory usage.

Question 30: What will be the output of the following program?

public static void Main()
{
	StringBuilder sb = new StringBuilder();
	sb = "Hello";
		
	Console.WriteLine(sb);
}

Answer: C.

String cannot be assigned to StringBuilder directly. Use the Append() or AppendLine() method to append strings in the StringBuilder.