String comparison and equality in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this string equality check?

Consider the following C# code snippet. What will be printed to the console?

C Sharp (C#)

string a = "Hello";
string b = "hello";
Console.WriteLine(a == b);

A False

B True

C Compilation error

D Runtime exception

💡 Hint

Remember that string equality with == is case-sensitive by default.

The == operator compares strings with case sensitivity, so "Hello" and "hello" are not equal.

❓ Predict Output

intermediate

What does this code print when comparing strings ignoring case?

What will be the output of this C# code?

C Sharp (C#)

string a = "Test";
string b = "test";
bool result = string.Equals(a, b, StringComparison.OrdinalIgnoreCase);
Console.WriteLine(result);

A Compilation error

B False

C True

D Runtime exception

💡 Hint

Check the StringComparison option used in string.Equals.

Using StringComparison.OrdinalIgnoreCase makes the comparison ignore case differences, so the strings are equal.

❓ Predict Output

advanced

What is the output of this string reference comparison?

Analyze the following C# code and determine what it prints.

C Sharp (C#)

string s1 = "hello";
string s2 = new string(new char[] {'h','e','l','l','o'});
Console.WriteLine(object.ReferenceEquals(s1, s2));

A False

B Compilation error

C Runtime exception

D True

💡 Hint

ReferenceEquals checks if both variables point to the same object in memory.

s1 and s2 have the same content but are different objects, so ReferenceEquals returns false.

❓ Predict Output

advanced

What does this code print when comparing strings with Compare method?

What will be the output of this C# code snippet?

C Sharp (C#)

string a = "apple";
string b = "banana";
int result = string.Compare(a, b, StringComparison.Ordinal);
Console.WriteLine(result);

A Compilation error

B Zero

C A positive number

D A negative number

💡 Hint

Compare returns a negative number if the first string is less than the second.

"apple" comes before "banana" lexicographically, so Compare returns a negative number.

❓ Predict Output

expert

What is the output of this culture-sensitive string comparison?

Consider this C# code. What will it print?

C Sharp (C#)

using System.Globalization;
System.Threading.Thread.CurrentThread.CurrentCulture = new System.Globalization.CultureInfo("de-DE");

string s1 = "straße";
string s2 = "strasse";
bool result = string.Equals(s1, s2, StringComparison.CurrentCultureIgnoreCase);
Console.WriteLine(result);

A False

B True

C Compilation error

D Runtime exception

💡 Hint

In German culture, "ß" is considered equivalent to "ss" in comparisons.

Using CurrentCultureIgnoreCase with German culture treats "straße" and "strasse" as equal ignoring case.

Practice

1. Which of the following is the correct way to check if two strings str1 and str2 have the same value in C#?

easy

A. if (str1 == str2)

B. if (str1 = str2)

C. if (str1.Equals)

D. if (str1.CompareTo(str2))

Solution

1. Step 1: Understand string equality operator

   In C#, == compares the values of two strings correctly.

2. Step 2: Analyze other options

   str1 = str2 is assignment, str1.Equals is incomplete, and CompareTo returns an int, not a bool.

3. Final Answer:

   if (str1 == str2) -> Option A

4. Quick Check:

   Use == for string equality [OK]

Hint: Use == to compare string values directly [OK]

Common Mistakes:

• Using single = instead of ==
• Calling Equals without parentheses or arguments
• Using CompareTo expecting a boolean

2. Which of the following is the correct syntax to compare two strings a and b ignoring case in C#?

easy

A. a.Equals(b)

B. a == b.ToLower()

C. string.Equals(a, b, StringComparison.OrdinalIgnoreCase)

D. string.Compare(a, b)

Solution

1. Step 1: Identify case-insensitive comparison method

   string.Equals with StringComparison.OrdinalIgnoreCase compares strings ignoring case.

2. Step 2: Check other options

   a == b.ToLower() compares different types, a.Equals(b) is case-sensitive, and string.Compare returns int, not bool.

3. Final Answer:

   string.Equals(a, b, StringComparison.OrdinalIgnoreCase) -> Option C

4. Quick Check:

   Use string.Equals with OrdinalIgnoreCase for case-insensitive [OK]

Hint: Use string.Equals with OrdinalIgnoreCase to ignore case [OK]

Common Mistakes:

• Using == which is case-sensitive
• Calling Equals without StringComparison argument
• Using string.Compare expecting boolean

3. What is the output of the following C# code?

string s1 = "apple";
string s2 = "Banana";
int result = string.Compare(s1, s2, StringComparison.OrdinalIgnoreCase);
Console.WriteLine(result);

medium

A. -1

B. 0

C. 1

D. Compilation error

Solution

1. Step 1: Understand string.Compare with OrdinalIgnoreCase

   It compares strings ignoring case and returns negative if first is before second alphabetically.

2. Step 2: Compare "apple" and "Banana" ignoring case

   "apple" comes before "banana" alphabetically, so result is negative (-1).

3. Final Answer:

   -1 -> Option A

4. Quick Check:

   "apple" < "Banana" ignoring case = -1 [OK]

Hint: Compare returns negative if first string is alphabetically before second [OK]

Common Mistakes:

• Assuming Compare returns boolean
• Ignoring case sensitivity in comparison
• Expecting 0 when strings differ

4. The following code is intended to check if two strings are equal ignoring case, but it does not work as expected. What is the error?

string a = "Hello";
string b = "hello";
if (a == b.ToLower())
{
    Console.WriteLine("Equal");
} else {
    Console.WriteLine("Not Equal");
}

medium

A. The code should use 'string.Compare(a, b)' without ToLower()

B. b.ToLower() returns null, causing error

C. The code should use 'a.Equals(b)' instead

D. Using '==' compares case-sensitively, so it fails here

Solution

1. Step 1: Analyze '==' operator behavior

   The '==' operator compares strings case-sensitively, so "Hello" != "hello".

2. Step 2: Understand why ToLower() doesn't fix it

   Comparing 'a' to 'b.ToLower()' still compares case-sensitively; 'a' is "Hello" (mixed case), so comparison fails.

3. Final Answer:

   Using '==' compares case-sensitively, so it fails here -> Option D

4. Quick Check:

   '==' is case-sensitive, so this check fails [OK]

Hint: Use string.Equals with ignore case instead of == [OK]

Common Mistakes:

• Assuming ToLower() changes original string
• Using == for case-insensitive comparison
• Not calling Equals with StringComparison argument

5. You want to sort a list of strings alphabetically ignoring case in C#. Which approach correctly compares two strings x and y inside a custom comparer?

hard

A. return x == y ? 0 : 1;

B. return string.Compare(x, y, StringComparison.OrdinalIgnoreCase);

C. return x.Equals(y) ? 0 : -1;

D. return x.CompareTo(y);

Solution

1. Step 1: Understand sorting comparer requirements

   A comparer must return negative, zero, or positive int based on alphabetical order.

2. Step 2: Check each option's return value and case sensitivity

   return string.Compare(x, y, StringComparison.OrdinalIgnoreCase); uses string.Compare with OrdinalIgnoreCase, correctly returning int for sorting ignoring case. return x == y ? 0 : 1; returns only 0 or 1, not suitable. return x.Equals(y) ? 0 : -1; returns 0 or -1 but ignores order and case. return x.CompareTo(y); uses CompareTo which is case-sensitive.

3. Final Answer:

   return string.Compare(x, y, StringComparison.OrdinalIgnoreCase); -> Option B

4. Quick Check:

   Use string.Compare with OrdinalIgnoreCase for case-insensitive sorting [OK]

Hint: Use string.Compare with OrdinalIgnoreCase in sorting comparer [OK]

Common Mistakes:

• Returning only 0 or 1 instead of negative/zero/positive
• Using case-sensitive CompareTo for ignoring case
• Using Equals which returns bool, not int