int score = 85;

if (score >= 90)
{
    Console.WriteLine("Grade: A");
}
else if (score >= 80)
{
    Console.WriteLine("Grade: B");
}
else
{
    Console.WriteLine("Grade: C or below");
}

Grade: B

int score = 95;

if (score >= 60)
{
    Console.WriteLine("Grade: D or better");
}
else if (score >= 90)
{
    Console.WriteLine("Grade: A");
}

Grade: D or better

if (false)
{
    Console.WriteLine("never");
}

Console.WriteLine("done");

1-13-storm.cs(3,5): warning CS0162: Unreachable code detected
done

int score = 95;

if (score >= 90)
{
    Console.WriteLine("A");
}
if (score >= 80)
{
    Console.WriteLine("B");
}
if (score >= 60)
{
    Console.WriteLine("D or better");
}

A
B
D or better

'F' → Fullscreen

Build

Everything today goes in a new program named 1-13-storm.

Task 1: Three Branches

• Write the code below and run it.
• Test all three branches by editing windSpeed: try 80, then 46, then 5. Write down what each one prints.
• Exactly one category prints every time. That is the chain doing its job — 80 is also greater than 39, and the tropical-storm branch was never even checked.
• Set it back to 46 before you continue.

1
int windSpeed = 46;
2

3
Console.WriteLine($"Wind speed: {windSpeed}");
4

5
if (windSpeed >= 74)
6
{
7
    Console.WriteLine("Category: hurricane");
8
}
9
else if (windSpeed >= 39)
10
{
11
    Console.WriteLine("Category: tropical storm");
12
}
13
else
14
{
15
    Console.WriteLine("Category: calm");
16
}

Task 2: The Full Scale

• Expand the chain to all seven branches.
• Notice the order: highest threshold first, working down. That is not a style choice. Reverse it and almost every branch becomes unreachable.
• Test at least four different speeds, including one above 157 and one below 39.

1
int windSpeed = 46;
2

3
Console.WriteLine($"Wind speed: {windSpeed}");
4

5
if (windSpeed >= 157)
6
{
7
    Console.WriteLine("Category: 5 - catastrophic");
8
}
9
else if (windSpeed >= 130)
10
{
11
    Console.WriteLine("Category: 4 - extreme");
12
}
13
else if (windSpeed >= 111)
14
{
15
    Console.WriteLine("Category: 3 - devastating");
16
}
17
else if (windSpeed >= 96)
18
{
19
    Console.WriteLine("Category: 2 - extensive");
20
}
21
else if (windSpeed >= 74)
22
{
23
    Console.WriteLine("Category: 1 - dangerous");
24
}
25
else if (windSpeed >= 39)
26
{
27
    Console.WriteLine("Category: tropical storm");
28
}
29
else
30
{
31
    Console.WriteLine("Category: calm");
32
}

Task 3: Plan, Then Classify Some Input

• The comments describe a rainfall scale with four categories. Write the code under them, leaving the comments where they are.
• Convert the input before you compare it. Same as Activity 1.12.
• Exactly one category must print, so this needs a chain and not separate ifs.
• Work out your ordering before you type it. Writing the four thresholds down on paper first is not cheating.

1
int windSpeed = 46;
2

3
Console.WriteLine($"Wind speed: {windSpeed}");
4

5
if (windSpeed >= 157)
6
{
7
    Console.WriteLine("Category: 5 - catastrophic");
8
}
9
else if (windSpeed >= 130)
10
{
11
    Console.WriteLine("Category: 4 - extreme");
12
}
13
else if (windSpeed >= 111)
14
{
15
    Console.WriteLine("Category: 3 - devastating");
16
}
17
else if (windSpeed >= 96)
18
{
19
    Console.WriteLine("Category: 2 - extensive");
20
}
21
else if (windSpeed >= 74)
22
{
23
    Console.WriteLine("Category: 1 - dangerous");
24
}
25
else if (windSpeed >= 39)
26
{
27
    Console.WriteLine("Category: tropical storm");
28
}
29
else
30
{
31
    Console.WriteLine("Category: calm");
32
}
33

34
Console.WriteLine();
35

36
// Ask the user for a rainfall total in millimeters and convert it
37
// 200 or more is "flood risk"
38
// 50 or more is "heavy"
39
// 10 or more is "moderate"
40
// anything else is "light"
41
// Display the rainfall, then its single category

Task 4: Kill a Branch on Purpose

Reorder your rainfall chain so that the flood risk branch can never run, no matter what the user types. You are allowed to move lines, not to delete them.

1. Run it with a rainfall of 400 and write down what it says instead.
2. Write down every warning the compiler gave you. If there were none, write “none” — that is the answer this task is looking for.
3. Write a comment in your file naming which line made the branch dead, and why the program still built.
4. Put the chain back in working order before you submit.

Challenge (Optional): Two Answers at Once

• At the very bottom of your program, add a second copy of the rainfall chain with every else removed — so it becomes three or four separate if statements.
• Run it with a rainfall of 400 and note how many lines print.
• Write a comment describing a rainfall report where you would want that behavior instead of a single category.
• Delete the extra copy before submitting.

Same Idea, Exam Notation

This is the biggest difference between the two notations in the whole course — and it is the one Activity 1.12 promised you.

The exam reference sheet has no ELSE IF. It offers IF and it offers IF/ELSE, and that is all. A chain has to be built by putting a whole new IF inside the ELSE block.

if (score >= 90)
{
    Console.WriteLine("A");
}
else if (score >= 80)
{
    Console.WriteLine("B");
}
else
{
    Console.WriteLine("C");
}

IF(score ≥ 90)
{
  DISPLAY("A")
}
ELSE
{
  IF(score ≥ 80)
  {
    DISPLAY("B")
  }
  ELSE
  {
    DISPLAY("C")
  }
}

Read the right-hand side carefully. The second IF is not a sibling of the first — it lives inside the first one's ELSE, indented a level deeper. The closing braces stack up at the bottom.

Why This Matters on Exam Day

• The nesting grows with every branch. Three branches means two levels. Seven branches, like your Task 2, would mean six levels and a wall of closing braces at the end.
• Exam questions look harder than they are. When you meet a deeply indented block of IF/ELSE, it is very often just a chain, written the only way the notation allows.
• The logic is identical. First match wins, exactly as in C#. Read it as a chain even though it is drawn as a nest.

A useful trick when you are tracing one of these: find the deepest ELSE and read it as “none of the conditions above were true.”

Checkpoint

Your finished program should run like this.

Wind speed: 46
Category: tropical storm

Rainfall in mm? 64 [Enter]
Rainfall: 64
Category: heavy

• Test your rainfall chain at 4, 25, 120, and 400. Each one should give a different category. If two of them agree, one of your branches is unreachable.
• All three Task 1 speeds are written down, and each printed exactly one category.
• Four different wind speeds were tested in Task 2, including one above 157 and one below 39.
• Task 4's dead-branch result is written down, including the number of warnings the compiler gave.
• Your rainfall chain is back in working order.

Reflection

Answer the following questions before submitting your work.

1. A score of 95 was reported as “D or better.” Explain what went wrong, and why C# gave no warning even though it has one for unreachable code.
2. Describe a situation where you would want separate if statements instead of a chain.
3. The exam notation has no else if, so chains are written as nested blocks. Does that change what the program does? Explain your answer.

Submit

Submit four things to the dropbox:

1. Your 1-13-storm program file, with the rainfall chain working.
2. Your Task 1 and Task 2 test results, and one full run of the finished program.
3. Your Task 4 result: what a rainfall of 400 reported, how many warnings you got, and which line killed the branch.
4. Your three reflection answers.

Activity Complete