TryParse for safe conversion in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to safely convert a string to an integer using TryParse.

C Sharp (C#)

int number;
bool success = int.[1]("123", out number);

Drag options to blanks, or click blank then click option'

ATryParse

BToInt32

CParse

DConvert

Attempts:

3 left

💡 Hint

Common Mistakes

Using Parse which throws an exception on failure.

Using Convert which throws exceptions for invalid input.

The TryParse method attempts to convert the string to an integer safely without throwing an exception if it fails.

2fill in blank

medium

Complete the code to check if the string "456" can be converted to an integer.

C Sharp (C#)

if (int.[1]("456", out int result))
{
    Console.WriteLine("Conversion succeeded: " + result);
}

Drag options to blanks, or click blank then click option'

AToInt32

BConvert

CParse

DTryParse

Attempts:

3 left

💡 Hint

Common Mistakes

Using Parse which throws exceptions instead of returning a boolean.

Not using the out keyword for the result parameter.

TryParse returns true if conversion succeeds, allowing safe checking before using the result.

3fill in blank

hard

Fix the error in the code to safely convert a string to a double using TryParse.

C Sharp (C#)

double value;
bool success = double.[1]("12.34", out value);

Drag options to blanks, or click blank then click option'

AToDouble

BTryParse

CConvert

DParse

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the out keyword causes a compile error.

Using Parse which throws exceptions on invalid input.

TryParse requires the second argument to be passed with the out keyword to store the converted value.

4fill in blank

hard

Fill both blanks to create a dictionary with word lengths only for words longer than 4 characters.

C Sharp (C#)

var words = new List<string> { "apple", "cat", "banana", "dog" };
var lengths = new Dictionary<string, int> { { "length", 0 } };
lengths = words.ToDictionary(word => word, word => word.[1]);
var filtered = lengths.Where(kv => kv.Value [2] 4).ToDictionary(kv => kv.Key, kv => kv.Value);

Drag options to blanks, or click blank then click option'

ALength

BCount

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using Count which is not a string property.

Using < instead of > causing wrong filtering.

Use Length to get the length of each word and filter with > to keep words longer than 4 characters.

5fill in blank

hard

Fill all three blanks to create a dictionary of uppercase words and their lengths, filtering only words longer than 3 characters.

C Sharp (C#)

var words = new List<string> { "tree", "sun", "flower", "sky" };
var result = words.Where(word => word.[3] [1] 3)
                  .ToDictionary(word => word.[2](), word => word.[3]);

Drag options to blanks, or click blank then click option'

ALength

B>

CToUpper

DCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using Count instead of Length for string length.

Not using parentheses for ToUpper method call.

Using < instead of > in the filter.

Filter words with length greater than 3, convert keys to uppercase with ToUpper(), and use Length for values.

Practice

1. What does int.TryParse return when the input string cannot be converted to an integer?

easy

A. It returns true and sets the output to zero.

B. It throws a FormatException error.

C. It returns false and does not throw an error.

D. It returns null.

Solution

1. Step 1: Understand TryParse behavior on invalid input

   TryParse attempts to convert a string to a number safely without throwing exceptions.

2. Step 2: Check return value when conversion fails

   If the string is not a valid number, TryParse returns false and does not throw an error.

3. Final Answer:

   It returns false and does not throw an error. -> Option C

4. Quick Check:

   TryParse returns false on failure [OK]

Hint: TryParse returns false, no exceptions on bad input [OK]

Common Mistakes:

• Thinking TryParse throws exceptions on bad input
• Assuming TryParse returns true even if conversion fails
• Confusing TryParse with Parse which throws errors

2. Which of the following is the correct syntax to safely convert a string input to an integer using int.TryParse?

easy

A. int.TryParse(input, out int result);

B. int result = int.TryParse(input);

C. int result = int.Parse(input);

D. int.TryParse(out int result, input);

Solution

1. Step 1: Recall TryParse method signature

   TryParse takes the input string first, then an out parameter for the result.

2. Step 2: Identify correct syntax

   int.TryParse(input, out int result); matches the correct order and usage: int.TryParse(input, out int result);

3. Final Answer:

   int.TryParse(input, out int result); -> Option A

4. Quick Check:

   TryParse(input, out result) syntax [OK]

Hint: TryParse syntax: input first, then out variable [OK]

Common Mistakes:

• Swapping input and out parameter order
• Assigning TryParse result directly to int
• Using Parse syntax instead of TryParse

3. What will be the output of the following code?

string input = "123";
bool success = int.TryParse(input, out int number);
Console.WriteLine(success);
Console.WriteLine(number);

medium

A. True
123

B. False
0

C. True
0

D. False
123

Solution

1. Step 1: Analyze TryParse with valid numeric string

   The string "123" is a valid integer, so TryParse returns true and sets number to 123.

2. Step 2: Check Console.WriteLine outputs

   First line prints success (true), second line prints number (123).

3. Final Answer:

   True 123 -> Option A

4. Quick Check:

   Valid input means success=true and number=parsed value [OK]

Hint: Valid number string makes TryParse return true and parsed value [OK]

Common Mistakes:

• Assuming TryParse returns false for valid numbers
• Expecting number to be zero even if success is true
• Confusing TryParse with Parse throwing exceptions

4. Identify the error in this code snippet:

string input = "abc";
int number;
bool success = int.TryParse(input, number);
Console.WriteLine(success);

medium

A. TryParse cannot be used with string variables.

B. Missing 'out' keyword before 'number' in TryParse call.

C. int number should be initialized before TryParse.

D. input string "abc" is invalid for TryParse.

Solution

1. Step 1: Check TryParse method call parameters

   TryParse requires the second argument to be passed with the 'out' keyword.

2. Step 2: Identify missing 'out' keyword

   The code passes 'number' without 'out', causing a compile error.

3. Final Answer:

   Missing 'out' keyword before 'number' in TryParse call. -> Option B

4. Quick Check:

   TryParse needs 'out' for output variable [OK]

Hint: Always use 'out' before variable in TryParse [OK]

Common Mistakes:

• Forgetting 'out' keyword in TryParse
• Trying to assign TryParse directly to int
• Assuming TryParse initializes variable without 'out'

5. You want to safely convert a list of strings inputs to integers, ignoring invalid entries. Which code snippet correctly uses int.TryParse to achieve this?

hard

A. List<int> numbers = new();
foreach (var s in inputs)
{
int.TryParse(s, out int n);
numbers.Add(n);
}

B. List<int> numbers = new();
foreach (var s in inputs)
{
int n = int.Parse(s);
numbers.Add(n);
}

C. List<int> numbers = inputs.Select(s => int.Parse(s)).ToList();

D. List<int> numbers = new();
foreach (var s in inputs)
{
if (int.TryParse(s, out int n))
numbers.Add(n);
}

Solution

1. Step 1: Understand safe conversion with TryParse in a loop

   We want to add only successfully parsed integers to the list, ignoring invalid strings.

2. Step 2: Analyze each option for correctness

   List<int> numbers = new(); foreach (var s in inputs) { if (int.TryParse(s, out int n)) numbers.Add(n); } uses TryParse with an if check to add only valid integers. List<int> numbers = new(); foreach (var s in inputs) { int n = int.Parse(s); numbers.Add(n); } and C use Parse which throws exceptions on invalid input. List<int> numbers = new(); foreach (var s in inputs) { int.TryParse(s, out int n); numbers.Add(n); } adds all results without checking success, adding zeros for invalid inputs.

3. Final Answer:

   List<int> numbers = new(); foreach (var s in inputs) { if (int.TryParse(s, out int n)) numbers.Add(n); } -> Option D

4. Quick Check:

   Use if (TryParse) to add valid numbers only [OK]

Hint: Use if (TryParse) to add only valid parsed numbers [OK]

Common Mistakes:

• Using Parse without try-catch causing exceptions
• Adding parsed number without checking TryParse success
• Assuming TryParse returns parsed number directly