C# Loop MCQs

Question 1: What will be the output of the following program?

int i = 0;

for(;;)
{
    if (i < 5)
            Console.Write(i);
    else
        break;
	i++;
}

Answer: A

for(;;) is perfectly valid. The initializer, condition and steps part can be placed out of the for loop.

Learn C# for loop.

Question 2: What will be the output of the following program?

for (double d = 1.01D; d < 1.05; d+= 0.01D)
{
    Console.Write("{0}, ", d);
}

Answer: C

Any integer data type can be used with the for loop. Learn C# for loop.

Question 3: What will be the output of the following program? 

public static void Main()
{
	while (ProcessMessage());
}
	
static bool ProcessMessage() {
	Console.Write("Hello");
	return false;
}

Answer: C

The while loop can be without any code block.

Question 4: What will be the output of the following program?

int i = 15;

for( ; ; )
{
    Console.Write("{0} ",i); 
    if (i >= -5)
        i -= 5; 
    else 
        break;
}

Answer: D

Question 5: What will be the output of the following program?:

public static void Main(string[] args)
{
	string str = "Hello";
		
    for(int i = 0; i<str.Length; i++)
        Console.WriteLine(str[i]);
}

Answer: D

String is an array of characters. So we can access it like an array. Learn C# Strings in detail.

Question 6: What will be the output of the following program?

static void Main()
{
    foreach (int number in GetNumbers())
    {
        Console.Write(number.ToString() + " ");
    }
}

public static System.Collections.IEnumerable GetNumbers()
{
    yield return 10;
    yield return 20;
    yield return 30;
}

Answer: B

Here, the first iteration of the foreach loop in the Main() method executes the GetNumbers() method until the first yield return statement is reached. This iteration returns 10, and the current location in the iterator method is retained. On the next iteration, execution in the iterator method continues from where it left off, again stopping when it reaches a yield return statement. This iteration returns 20, and the current location in the iterator method is again retained. The loop completes when the end of the iterator method is reached.

Learn more about iterators.

Question 7: What will be the output of the following program?

static void Main()
{
    foreach (int number in GetNumbers())
    {
        // do nothing
    }
}

public static System.Collections.IEnumerable GetNumbers()
{
    Console.Write("yield-1 ");
    yield return 10;

    Console.Write("yield-2 ");
    yield return 20;

    Console.Write("yield-3");
    yield return 30;
}

Answer: D

Here, the first iteration of a foreach loop in the Main() method executes the GetNumbers() method until the first yield return statement is reached. This iteration prints "yield-1" and returns 10, and the current location in the iterator method is retained. On the next iteration, execution in the iterator method continues from where it left off, again stopping when it reaches a yield return statement. This iteration prints "yield-2" and returns 20, and the current location in the iterator method is again retained. The loop completes when the end of the iterator method is reached.

Learn more about iterators.