Enum parsing from strings in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Enum parsing code?

Consider the following C# code that parses a string into an enum value. What will be printed?

C Sharp (C#)

using System;

enum Color { Red, Green, Blue }

class Program {
    static void Main() {
        string input = "Green";
        if (Enum.TryParse<Color>(input, out var color)) {
            Console.WriteLine((int)color);
        } else {
            Console.WriteLine("Parse failed");
        }
    }
}

A 1

B 0

C Parse failed

D 2

💡 Hint

Remember that enum values start at 0 by default and increment by 1.

The enum Color has Red=0, Green=1, Blue=2. Parsing "Green" succeeds and returns the enum value with underlying int 1.

❓ Predict Output

intermediate

What happens if parsing fails without TryParse?

What will happen when running this code?

C Sharp (C#)

using System;

enum Status { Active, Inactive }

class Program {
    static void Main() {
        string input = "Pending";
        var status = (Status)Enum.Parse(typeof(Status), input);
        Console.WriteLine(status);
    }
}

A Throws ArgumentException

B Prints 0

C Prints Pending

D Prints Active

💡 Hint

Enum.Parse throws an exception if the string does not match any enum name.

Since "Pending" is not a member of the Status enum, Enum.Parse throws an ArgumentException.

🔧 Debug

advanced

Why does this Enum.TryParse fail unexpectedly?

Look at this code snippet. It tries to parse a string to an enum but always fails. Why?

C Sharp (C#)

using System;

enum Direction { North, South, East, West }

class Program {
    static void Main() {
        string input = "north";
        if (Enum.TryParse<Direction>(input, out var dir)) {
            Console.WriteLine(dir);
        } else {
            Console.WriteLine("Failed to parse");
        }
    }
}

A The out variable dir is not declared correctly

B The enum Direction does not contain "north" because it is misspelled

C Enum.TryParse is case-sensitive by default, so "north" does not match "North"

D Enum.TryParse requires a third boolean parameter to work

💡 Hint

TryParse can be case-insensitive if you specify an option.

By default, Enum.TryParse is case-insensitive. The string "north" does not match the enum member "North" because of case difference.

📝 Syntax

advanced

Which option correctly parses a string ignoring case?

Choose the code snippet that correctly parses the string "west" to the enum Direction ignoring case.

C Sharp (C#)

enum Direction { North, South, East, West }

A Enum.TryParse<Direction>("west", out var d);

B Enum.Parse(typeof(Direction), "west", false);

C Enum.Parse<Direction>("west", true);

D Enum.TryParse<Direction>("west", out var d, true);

💡 Hint

Look for the overload of TryParse that accepts a boolean for case-insensitivity.

Option D uses Enum.TryParse with the third parameter ignoreCase=true, which allows parsing "west" ignoring case.

🚀 Application

expert

How many items are in the dictionary after parsing multiple enum strings?

Given this code, how many key-value pairs does the dictionary contain after execution?

C Sharp (C#)

using System;
using System.Collections.Generic;

enum Level { Low = 1, Medium = 2, High = 3 }

class Program {
    static void Main() {
        string[] inputs = { "Low", "Medium", "High", "low", "HIGH" };
        var dict = new Dictionary<Level, int>();
        foreach (var s in inputs) {
            if (Enum.TryParse<Level>(s, true, out var level)) {
                if (!dict.ContainsKey(level)) {
                    dict[level] = 0;
                }
                dict[level]++;
            }
        }
        Console.WriteLine(dict.Count);
    }
}

A 5

B 3

C 2

D 4

💡 Hint

Consider that parsing is case-insensitive and dictionary keys are unique enum values.

All strings parse to one of three enum values: Low, Medium, High. Case differences do not create new keys. So dictionary has 3 keys.

Practice

1. What does Enum.Parse do in C#?

easy

A. Checks if a string is a valid enum name without converting

B. Converts an enum value to a string

C. Creates a new enum type at runtime

D. Converts a string to the corresponding enum value

Solution

1. Step 1: Understand Enum.Parse purpose

   Enum.Parse takes a string and tries to convert it to the matching enum value.

2. Step 2: Compare options

   Only Converts a string to the corresponding enum value describes converting string to enum value. Others describe different actions.

3. Final Answer:

   Converts a string to the corresponding enum value -> Option D

4. Quick Check:

   Enum.Parse converts string to enum [OK]

Hint: Enum.Parse converts string to enum value directly [OK]

Common Mistakes:

• Thinking Enum.Parse converts enum to string
• Confusing Enum.Parse with Enum.TryParse
• Believing Enum.Parse checks validity without conversion

2. Which of the following is the correct syntax to parse a string "Monday" to an enum DayOfWeek using Enum.Parse?

easy

A. DayOfWeek day = Enum.Parse("Monday");

B. DayOfWeek day = (DayOfWeek)Enum.Parse(typeof(DayOfWeek), "Monday");

C. DayOfWeek day = Enum.Parse(DayOfWeek, "Monday");

D. DayOfWeek day = Enum.TryParse("Monday", out DayOfWeek day);

Solution

1. Step 1: Recall Enum.Parse syntax

   The correct syntax requires specifying the enum type with typeof and casting the result.

2. Step 2: Analyze options

   DayOfWeek day = (DayOfWeek)Enum.Parse(typeof(DayOfWeek), "Monday"); matches the correct syntax: cast the result of Enum.Parse(typeof(EnumType), string).

3. Final Answer:

   DayOfWeek day = (DayOfWeek)Enum.Parse(typeof(DayOfWeek), "Monday"); -> Option B

4. Quick Check:

   Enum.Parse needs typeof and cast [OK]

Hint: Use typeof(Enum) and cast result for Enum.Parse [OK]

Common Mistakes:

• Omitting typeof(EnumType)
• Not casting the result to enum type
• Confusing Enum.Parse with Enum.TryParse syntax

3. What will be the output of this code?

enum Color { Red, Green, Blue }

string input = "Green";
Color c = (Color)Enum.Parse(typeof(Color), input);
Console.WriteLine(c);

medium

A. Green

B. Runtime error

C. Blue

D. Red

Solution

1. Step 1: Parse string to enum

   The string "Green" matches the enum member Color.Green, so Enum.Parse returns that value.

2. Step 2: Print enum value

   Console.WriteLine prints the enum member name, which is "Green".

3. Final Answer:

   Green -> Option A

4. Quick Check:

   Enum.Parse("Green") = Color.Green [OK]

Hint: Enum.Parse returns enum matching string name [OK]

Common Mistakes:

• Expecting numeric value instead of name
• Assuming case-insensitive parsing by default
• Thinking it throws error for valid names

4. What is wrong with this code snippet?

enum Status { Active, Inactive }

string input = "Pending";
Status s = (Status)Enum.Parse(typeof(Status), input);
Console.WriteLine(s);

medium

A. It will print "Pending"

B. It will parse to Status.Active by default

C. It will throw a runtime exception

D. It will return null

Solution

1. Step 1: Check if input matches enum members

   The string "Pending" is not a member of Status enum, so Enum.Parse cannot convert it.

2. Step 2: Understand Enum.Parse behavior on invalid input

   Enum.Parse throws a runtime exception if the string does not match any enum name.

3. Final Answer:

   It will throw a runtime exception -> Option C

4. Quick Check:

   Invalid string causes Enum.Parse exception [OK]

Hint: Enum.Parse throws error if string not in enum [OK]

Common Mistakes:

• Expecting default enum value on invalid string
• Thinking it returns null instead of error
• Confusing with Enum.TryParse behavior

5. You want to safely convert a string "Sunday" to enum DayOfWeek without risking exceptions. Which code snippet correctly does this?

hard

A. bool success = Enum.TryParse("Sunday", true, out DayOfWeek day);

B. DayOfWeek.TryParse("Sunday", out DayOfWeek day);

C. Enum.TryParse(typeof(DayOfWeek), "Sunday", out DayOfWeek day);

D. DayOfWeek day = (DayOfWeek)Enum.Parse(typeof(DayOfWeek), "Sunday");

Solution

1. Step 1: Understand safe parsing with Enum.TryParse

   Enum.TryParse returns a bool indicating success and outputs the parsed enum value.

2. Step 2: Check correct method signature

   bool success = Enum.TryParse("Sunday", true, out DayOfWeek day); uses Enum.TryParse with ignoreCase=true and out parameter, matching correct safe parsing syntax.

3. Final Answer:

   bool success = Enum.TryParse("Sunday", true, out DayOfWeek day); -> Option A

4. Quick Check:

   Enum.TryParse with out and ignoreCase is safe [OK]

Hint: Use Enum.TryParse with out and ignoreCase for safe parse [OK]

Common Mistakes:

• Using Enum.Parse which throws exceptions
• Calling TryParse on enum type instead of Enum class
• Ignoring the out parameter requirement