String searching and extraction in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of IndexOf and Substring

What is the output of this C# code snippet?

C Sharp (C#)

string text = "Hello, world!";
int index = text.IndexOf('o');
string result = text.Substring(index, 5);
Console.WriteLine(result);

A ow ,o

B o, worl

C o, wo

D lrow ,o

💡 Hint

Remember that Substring's second parameter is length, not end index.

IndexOf('o') returns 4 (the first 'o' in "Hello"). Substring(4,5) extracts 5 characters starting at index 4: 'o, wo'.

❓ Predict Output

intermediate

Extracting domain from email

What is the output of this C# code?

C Sharp (C#)

string email = "[e-mail]";
int atPos = email.IndexOf('@');
string domain = email.Substring(atPos + 1);
Console.WriteLine(domain);

A user@

B [e-mail]

C @example.com

D example.com

💡 Hint

Substring starting after '@' extracts the domain part.

IndexOf('@') finds position of '@'. Substring(atPos + 1) extracts everything after '@', which is 'example.com'.

❓ Predict Output

advanced

Using Regex to extract numbers

What does this C# code print?

C Sharp (C#)

using System.Text.RegularExpressions;

string input = "Order1234: 56 items";
var match = Regex.Match(input, @"\d+");
Console.WriteLine(match.Value);

A 1234

B 56

C Order1234

D items

💡 Hint

Regex.Match finds the first sequence of digits.

The pattern \d+ matches one or more digits. The first such sequence in the string is '1234'.

❓ Predict Output

advanced

Extracting substring between two characters

What is the output of this C# code?

C Sharp (C#)

string data = "[start]middle[end]";
int startIndex = data.IndexOf('[') + 1;
int endIndex = data.IndexOf(']');
string extracted = data.Substring(startIndex, endIndex - startIndex);
Console.WriteLine(extracted);

A start]middle

B start

C start]middle[end

D start]middle[end]

💡 Hint

Substring extracts from after '[' up to before ']'.

IndexOf('[') returns 0, so startIndex is 1. IndexOf(']') returns 6. Substring(1, 5) extracts 'start'.

🧠 Conceptual

expert

Behavior of String.IndexOf with missing substring

What is the value of variable 'pos' after running this C# code?

C Sharp (C#)

string text = "hello world";
int pos = text.IndexOf("xyz");

A -1

B 0

C throws an exception

D length of the string

💡 Hint

IndexOf returns -1 if substring is not found.

When the substring is not found, IndexOf returns -1 instead of throwing an error or returning 0.