Objective

Four short programs about repetition — Activities 1.17 through 1.21.

All four of these compile. Not one of them produces an error, a warning, or a crash. Every one of them is wrong.

That is what makes loops worth a debug page of their own. A loop that repeats the wrong number of times, or changes the wrong variable, is still a perfectly legal loop — there is nothing for C# to object to, so you get a clean run and a confident wrong answer.

The Four Programs

Bug 1

This should count down from 5 to 1 and then say liftoff. It prints forever.

1
int count = 5;
2

3
while (count > 0)
4
{
5
    Console.WriteLine(count);
6
}
7

8
Console.WriteLine("Liftoff!");

Also: how would you know this loop never ends without running it? Say exactly what you looked for.

Bug 2

This should print the numbers 1 through 10. It prints 0 through 9.

1
for (int i = 0; i < 10; i++)
2
{
3
    Console.WriteLine(i);
4
}

Also: there is more than one way to fix this one. Give two, and say which you would rather read.

Bug 3

This should add up 1 + 2 + 3 + 4 + 5 and print 15. It prints 5.

1
int total = 0;
2

3
for (int i = 1; i <= 5; i++)
4
{
5
    total = i;
6
}
7

8
Console.WriteLine($"Total: {total}");

Bug 4

This should print a grid of stars — three rows of four. It prints twelve lines with one star on each.

1
for (int row = 1; row <= 3; row++)
2
{
3
    for (int col = 1; col <= 4; col++)
4
    {
5
        Console.WriteLine("* ");
6
    }
7
}

Also: the twelve is correct even though the output is not. Say where the twelve comes from.

Submit

For each program, give:

• One sentence on what was wrong
• The corrected line, or lines, of code

Plus the three written answers:

• Bug 1 — what you look for to spot a loop that never ends, without running it
• Bug 2 — two different fixes, and which you prefer
• Bug 4 — where the twelve comes from

Work them out by reading first. Running the code tells you that something is wrong; it rarely tells you why, and on the exam there is no computer.