Practicing while Loops – Warm-Up

Create a new project, and replace the content of the Main method with the following code:

int i = 0;
while(i < 100)
{
    Console.WriteLine(i);
    i++;
}

1. Execute the code. You should see the numbers 0 to 99 in the console.
2. Replace < with <=, and note that it prints the numbers from 0 to 100, even even though you did not change the numbers.
3. Replace 0 with 100 and 100 with 300, and note that it prints the numbers from 100 to 300. Observe that the counter can start from and terminate with any number you wish.
4. Modify the code such that it prints all integers between 0 and 100 that are divisible by 3. The solution is given below, but please attempt to do it independently before reading it.

int i = 0;
while(i < 100)
{
    if(i % 3 == 0)
        Console.WriteLine(i);
    i++;
}

int i = 0;
while(i < 100)
{
    Console.WriteLine(i);
    i += 3;
}

Practicing while Loops – Decrementing Counter

Create a new project and replace the content of the Main method with the following code:

int n = 100;
while (n > 0)
{
    Console.WriteLine(n);
    n--;
}

Execute the code, and explain what you see in the console. Note that the counter is decremented, not incremented.

Practicing while Loops – Mystery Program

Create a new project and replace the content of the Main method with the following code:

int n;
Console.Write("Enter a natural number greater than 2: ");
n = int.Parse(Console.ReadLine());
int i = 2;
while(n % i != 0 && i < n )
{
    i++;
}
if (i == n)
    Console.WriteLine($"{n} is a ... number");
else
    Console.WriteLine($"{n} is not a ... number");

1. What does the code do? Explain the boolean expression of the loop
2. Replace ... with a meaningful word.

Practicing while Loops – Summing User-Input

Write a program that asks for an integer value greater than 1 from the user, and computes the result of this series: 1 + 2 + 3 + 4 + ... up to n where n represents the number obtained from the user.

Here is an example of the desired execution, where the user input is underlined, and hitting “enter” is represented by ↵:

Please enter an integer greater than 1:
8̲↵
The sum from 1 to your number is: 36

Infinite Loops

All of the following are examples of infinite loops. Can you spot the “problem”? For each of them, suggest an edit that would make them terminate.

int number = 0;
while (number <=5) {
    Console.WriteLine("Hi!");
    Console.WriteLine(number);
}

int number1 = 0, number = 0;
while (number <=5) {
    Console.WriteLine("Hi!");
    Console.WriteLine(number);
    number1++;
}

int number = 0;
while (number <=5);
{
    Console.WriteLine("Hi!");
    Console.WriteLine(number);
    number++;
}

int number = 0;
while (number <=5)
Console.WriteLine("Hi!");
Console.WriteLine(number);
number++;

int number = 0;
while (number <= 5)
{
    Console.WriteLine("Hi!");
    Console.WriteLine(number);
}
number++;

int number = 0;
while (number <= 5)
{
    Console.WriteLine("Hi!");
    number--;
    Console.WriteLine(number);
    number++;
}

Pushing Further (Optional)

Here are two advanced while loop challenges. Try to think “off-keyboard” for a while before coding your solution, and test it extensively.

Console.WriteLine("Enter a number to sum, or \"Done\" to stop and print the total.");
string enter = Console.ReadLine();
int sum = 0;
while (enter != "Done")
{
    sum += int.Parse(enter);
    Console.WriteLine("Enter a number to sum, or \"Done\" to stop and print the total.");
    enter = Console.ReadLine();
}
Console.WriteLine($"Your total is {sum}.");