Basic for Loop Practice

Complete the following exercises related to for loops.

Exercise 1: Bugs

Visit each of the following Repls. Start by trying to run the programs, and make a note of any error messages received. Then, fork the Repl and try to fix the code!

• Bug 1
• Bug 2
• Bug 3
• Bug 4
• Bug 5

Exercise 2: Rocket Launch Countdown

Create a program that uses a for loop to count down the numbers from 10 to 1, then says "Lift off!"

1. Create a new project in Repl
2. In the body of the Main method, print out a message that says "Rocket Launch"
3. Under that, create a for loop

    for () { }
   

4. For the first part of the for loop (initializer), create an int i variable and set it to 10

    for (int i = 10;) { }
   

5. For the next part (conditional), check if i is greater than 0

    for (int i = 10; i > 0;) { }
   

6. For the final part (modifier), decrease the value of i by 1 with i--

    for (int i = 10; i > 0; i--) { }
   

7. In the body of the for loop (between the brackets), print the value of i

    Console.WriteLine(i);
   

8. Under the for loop, print a message that says "Lift off!"

Run the program, and verify that it counts down and says "Lift off!" at the end.

Bonus: Slow Counter

Right now, all of the countdown numbers appear pretty much at the same time. The computer moves too fast! It is actually possible to slow it down using the Thread.Sleep method. This will stop program execution for a given amount of time. This can be very helpful for programs that deal with timing of any kind.

1. At the top of the file, add using System.Threading;
2. In the body of the for loop, make a new line
3. Add Thread.Sleep(1000); to wait for 1000 ms (one second) before continuing

Run the program, and make sure the countdown is slowed down!

Exercise 3: Triangle of Zeroes

Create a program that can print a triangle consisting of powers of 10. It should ask the user how tall the triangle should be, and then print it out. This will be possible using the Math.Pow function to calculate each power of 10.

Examples

If the user entered 3, the program should print:

1
10
100

If the user entered 5, the program should print:

1
10
100
1000
10000

Note: This will not work for large inputs, because C# will truncate the numeric output

Implementation

Follow the steps below to implement the program.

1. Create a new project in Repl
2. In the body of the Main method, print out a message that says "How tall of a triangle?"
3. Under that, create a new int variable named height
4. Set the height variable to Convert.ToInt32(Console.ReadLine())
5. Under that, create a for loop

    for () { }
   

6. For the first part of the for loop (initializer), create an int i variable and set it to 0

    for (int i = 0;) { }
   

7. For the next part (conditional), check if i is less than the height variable

    for (int i = 0; i < height;) { }
   

8. For the final part (modifier), increase the value of i by 1 with i++

    for (int i = 0; i < height; i++) { }
   

9. In the body of the for loop, create a new double variable named power
10. Set the power variable to Math.Pow(10, i)
    • This will calculate the power of 10 for the given index
11. Use Console.WriteLine to print out the value of the power variable

Run the program, and verify that it properly prints out some triangles!

Exercise 4: Rainbow Road

Create a program that will print out a road that changes colors as it goes. This will be possible using a List of ConsoleColor values. Create a new Repl, and remove any code from the body of the Main method to get started.

The List<ConsoleColor>

First, create a new List of ConsoleColor values containing the colors of a rainbow: red, orange, yellow, green, blue, and purple. For convenience, the code for that is here:

List<ConsoleColor> colors = new List<ConsoleColor>()
{
    ConsoleColor.Red,
    ConsoleColor.DarkYellow,
    ConsoleColor.Yellow,
    ConsoleColor.Green,
    ConsoleColor.Blue,
    ConsoleColor.Magenta
};

Make sure to add using System.Collections.Generic; so the List works properly!

The Road

Follow the steps below to create the rainbow road.

1. Under the colors list, create a for loop that will loop through 15 times

    for (int i = 0; i < 15; i++) { }
   

2. In the body of the for loop, print out the text | || |
3. Run the program, and verify that a colorless road appears in the console
4. Back in the for loop body, make some new lines above the Console.WriteLine statement
5. At the top of the for loop body, create a new int variable named colorIndex
6. Set the colorIndex variable to i % colors.Count
   • This will allow the road to cycle through the colors multiple times
7. On the next line, create a new ConsoleColor variable named currentColor
8. Set the currentColor variable to the value in the colors list at colorIndex

    ConsoleColor currentColor = colors[colorIndex];
   

9. Under that, set the Console.ForegroundColor value to currentColor

    Console.ForegroundColor = currentColor;
   

Run the program again, and verify that a rainbow road appears! Feel free to change the length of the road by updating the 15 in the conditional part of the for loop.