Parsing input to numeric types in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to parse the input string to an integer.

C Sharp (C#)

string input = Console.ReadLine();
int number = int.Parse([1]);

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

Anumber

BConsole.ReadLine()

Cinput

DConvert.ToInt32(input)

Attempts:

3 left

💡 Hint

Common Mistakes

Using Console.ReadLine() directly inside int.Parse again causes double reading.

Trying to parse the variable number before it is assigned.

The int.Parse method converts the string input to an integer.

2fill in blank

medium

Complete the code to safely parse the input string to an integer using TryParse.

C Sharp (C#)

string input = Console.ReadLine();
if (int.TryParse([1], out int result))
{
    Console.WriteLine($"Parsed number: {result}");
}

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

Ainput

Bnumber

CConsole.ReadLine()

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the output variable result instead of the input string.

Calling Console.ReadLine() again inside TryParse.

int.TryParse tries to convert the string input to an integer safely.

3fill in blank

hard

Fix the error in the code to parse a double from input.

C Sharp (C#)

string input = Console.ReadLine();
double value = double.Parse([1]);

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

Avalue

Binput

CConsole.ReadLine()

Ddouble.TryParse(input, out value)

Attempts:

3 left

💡 Hint

Common Mistakes

Using the variable value before assignment.

Trying to use double.TryParse inside Parse.

The double.Parse method requires the string input variable to convert.

4fill in blank

hard

Fill both blanks to create a dictionary of word lengths for words longer than 3 characters.

C Sharp (C#)

string[] words = { "apple", "cat", "banana", "dog" };
var lengths = new Dictionary<string, int> { { [1], [2] } };

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

A"apple"

B"cat"

C5

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using numbers as keys or strings as values incorrectly.

Mixing up the order of key and value.

The dictionary needs a key (word) and a value (length). Here, "apple" and 5 are an example pair.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension with condition on word length.

C Sharp (C#)

string[] words = { "apple", "cat", "banana", "dog" };
var lengths = words.Where(w => w.Length > [1])
    .ToDictionary([2] => [3]);

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

A2

Bw

Cw.Length

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong number in the condition.

Swapping key and value in the dictionary.

The condition filters words longer than 3 letters. The dictionary uses the word as key and its length as value.

Practice

1.

Which method should you use in C# to convert a string to an integer when you are sure the string contains a valid number?

easy

A. int.TryParse(stringValue, out int result)

B. int.Parse(stringValue)

C. Convert.ToString(stringValue)

D. string.ToInt()

Solution

1. Step 1: Understand the purpose of Parse

   The method int.Parse converts a string directly to an integer if the string is a valid number.

2. Step 2: Compare with TryParse and others

   int.TryParse is used to safely check conversion but requires an out parameter; Convert.ToString converts to string, not number; string.ToInt() does not exist in C#.

3. Final Answer:

   int.Parse(stringValue) -> Option B

4. Quick Check:

   Use Parse when sure input is numeric [OK]

Hint: Use Parse when input is guaranteed numeric [OK]

Common Mistakes:

• Using TryParse without out parameter
• Using Convert.ToString to get a number
• Assuming string.ToInt() exists

2.

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

string input = "123";

easy

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

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

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

D. int result = TryParse(input);

Solution

1. Step 1: Recall TryParse syntax

   TryParse requires the keyword 'out' before the variable to store the parsed value.

2. Step 2: Check each option

   int.TryParse(input, out int result); uses 'out int result' correctly; others miss 'out' or assign TryParse's bool return to int.

3. Final Answer:

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

4. Quick Check:

   TryParse needs 'out' parameter [OK]

Hint: Remember TryParse needs 'out' before result variable [OK]

Common Mistakes:

• Omitting 'out' keyword
• Assigning TryParse result directly to int
• Using invalid method calls

3.

What will be the output of the following C# code?

string input = "456";
if (int.TryParse(input, out int number))
{
    Console.WriteLine(number + 10);
}
else
{
    Console.WriteLine("Invalid input");
}

medium

A. 45610

B. Invalid input

C. 466

D. Compilation error

Solution

1. Step 1: TryParse converts "456" to integer 456

   Since "456" is a valid number, TryParse returns true and sets number = 456.

2. Step 2: Add 10 and print result

   Inside the if block, number + 10 = 456 + 10 = 466, which is printed.

3. Final Answer:

   466 -> Option C

4. Quick Check:

   TryParse success adds 10 to 456 [OK]

Hint: TryParse returns true for valid numbers [OK]

Common Mistakes:

• Thinking TryParse returns the number directly
• Concatenating strings instead of adding numbers
• Assuming else block runs for valid input

4.

Identify the error in the following code snippet that tries to parse a string to an integer:

string input = "abc";
int number = int.Parse(input);
Console.WriteLine(number);

medium

A. No error, code runs fine

B. int.Parse returns 0 for invalid input

C. int.Parse converts "abc" to ASCII values

D. int.Parse throws an exception for non-numeric strings

Solution

1. Step 1: Understand int.Parse behavior

   int.Parse expects a valid numeric string; if input is "abc", it throws a FormatException.

2. Step 2: Check other options

   int.Parse does not return 0 or convert to ASCII; it throws an error, so code will not run fine.

3. Final Answer:

   int.Parse throws an exception for non-numeric strings -> Option D

4. Quick Check:

   Parse throws error on invalid input [OK]

Hint: Parse throws error if input is not numeric [OK]

Common Mistakes:

• Expecting Parse to return 0 on failure
• Ignoring exceptions from Parse
• Confusing Parse with TryParse

5.

You want to read a user input string and convert it to a double safely. Which code snippet correctly handles invalid input without crashing?

string userInput = Console.ReadLine();

hard

A. if (double.TryParse(userInput, out double value)) { Console.WriteLine(value); } else { Console.WriteLine("Invalid number"); }

B. double value = double.Parse(userInput);

C. double value = Convert.ToDouble(userInput);

D. double value = (double)userInput;

Solution

1. Step 1: Understand safe parsing with TryParse

   double.TryParse attempts to convert the string and returns true if successful, avoiding exceptions.

2. Step 2: Check each option for safety

   double value = double.Parse(userInput); and Convert.ToDouble(userInput) throw exceptions on invalid input; double value = (double)userInput; is invalid cast; if (double.TryParse(userInput, out double value)) { Console.WriteLine(value); } else { Console.WriteLine("Invalid number"); } safely checks and handles invalid input.

3. Final Answer:

   if (double.TryParse(userInput, out double value)) { Console.WriteLine(value); } else { Console.WriteLine("Invalid number"); } -> Option A

4. Quick Check:

   TryParse safely converts or handles errors [OK]

Hint: Use TryParse to avoid exceptions on bad input [OK]

Common Mistakes:

• Using Parse without try-catch
• Casting string directly to double
• Assuming Convert.ToDouble never fails