String comparison and equality in C Sharp (C#) - Step-by-Step Execution

Concept Flow - String comparison and equality

Start

↓

Get string1

↓

Get string2

↓

Compare strings

↓

Are strings equal?

Yes→Output: Equal

↓

Output: Not Equal

↓

End

This flow shows how two strings are taken, compared for equality, and then outputs if they are equal or not.

Execution Sample

C Sharp (C#)

string s1 = "Hello";
string s2 = "hello";
bool areEqual = s1 == s2;
Console.WriteLine(areEqual);

This code compares two strings for equality and prints True or False.

Execution Table

Step	Variable/Expression	Value	Condition/Check	Action/Output
1	s1	"Hello"	N/A	Assign string "Hello" to s1
2	s2	"hello"	N/A	Assign string "hello" to s2
3	areEqual = s1 == s2	False	Compare "Hello" == "hello"	Result is False because of case difference
4	Console.WriteLine(areEqual)	False	Print value of areEqual	Output: False

💡 Comparison done, output printed, program ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
s1	null	"Hello"	"Hello"	"Hello"	"Hello"
s2	null	null	"hello"	"hello"	"hello"
areEqual	undefined	undefined	undefined	False	False

Key Moments - 2 Insights

Why does s1 == s2 return False even though the words look similar?

Because string comparison in C# is case-sensitive by default, "Hello" and "hello" differ in letter case, so the comparison returns False as shown in step 3 of the execution_table.

Can we use == to compare strings safely in C#?

Yes, == compares string contents, not references, so it works for equality checks as shown in step 3. But it is case-sensitive.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of areEqual at step 3?

A False

B True

C null

D Undefined

💡 Hint

Check the 'Value' column at step 3 in execution_table.

At which step is the output printed to the console?

A Step 1

B Step 2

C Step 4

D Step 3

💡 Hint

Look for Console.WriteLine action in the execution_table.

If s2 was "Hello" instead of "hello", what would be the value of areEqual at step 3?

A False

B True

C null

D Undefined

💡 Hint

Consider how == compares strings case-sensitively as shown in step 3.

Concept Snapshot

String comparison in C# uses == to check if contents are equal.
Comparison is case-sensitive by default.
"Hello" == "hello" is False.
Use String.Equals with StringComparison for case-insensitive checks.
Console.WriteLine prints the boolean result.

Full Transcript

This example shows how two strings s1 and s2 are assigned values "Hello" and "hello" respectively. Then, the equality operator == compares them. Because C# string comparison is case-sensitive, the result is False. Finally, the program prints False to the console. Beginners often wonder why similar words are not equal; it's due to case sensitivity. The == operator compares string contents, not references, so it is safe for equality checks. If both strings had the same case, the result would be True.

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