String type and immutability in C Sharp (C#) - Step-by-Step Execution

Concept Flow - String type and immutability

Create string s = "hello"

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Strings stored in memory

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Modify s by s = s + " world"

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New string created: "hello world"

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s points to new string

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Old string "hello" unchanged

Strings in C# are stored in memory and cannot be changed after creation. When you modify a string, a new string is created and the variable points to it.

Execution Sample

C Sharp (C#)

string s = "hello";
s = s + " world";
Console.WriteLine(s);

This code creates a string, then modifies it by adding more text, showing that a new string is created.

Execution Table

Step	Variable	Value	Action	Note
1	s	"hello"	Assign string literal	s points to "hello"
2	s	"hello world"	Concatenate and assign	New string created, s updated
3	Output	"hello world"	Print s	Outputs the new string

💡 Program ends after printing the new string; original string "hello" remains unchanged in memory

Variable Tracker

Variable	Start	After 1	After 2	Final
s	null	"hello"	"hello world"	"hello world"

Key Moments - 2 Insights

Why does modifying the string create a new string instead of changing the original?

Because strings in C# are immutable, any change creates a new string object. See execution_table step 2 where s points to a new string after concatenation.

Does the original string "hello" get deleted after concatenation?

No, the original string stays in memory unchanged. The variable s just points to the new string. This is shown in the concept_flow where the old string remains.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of s after step 1?

A null

B "hello"

C "hello world"

D "world"

💡 Hint

Check the 'Value' column in execution_table row with Step 1

At which step does s point to the new string "hello world"?

A Step 2

B Step 1

C Step 3

D Never

💡 Hint

Look at the 'Action' and 'Value' columns in execution_table row Step 2

If strings were mutable, what would change in the execution_table?

A Step 1 would create two strings

B Step 3 would print null

C Step 2 would modify the existing string instead of creating a new one

D There would be no output

💡 Hint

Think about the meaning of immutability shown in concept_flow and execution_table step 2

Concept Snapshot

C# strings are immutable.
Any change creates a new string object.
Variables point to string objects.
Original strings remain unchanged.
Use + to concatenate creates new strings.
This helps with safety and performance.

Full Transcript

In C#, strings are special because once created, they cannot be changed. This is called immutability. When you write code like string s = "hello"; you create a string object with the text hello. If you then do s = s + " world";, you are not changing the original string. Instead, a new string object with the text "hello world" is created, and s now points to this new string. The old string "hello" stays in memory unchanged. This behavior helps avoid accidental changes and makes programs safer. The execution table shows each step: first s points to "hello", then after concatenation s points to "hello world", and finally the program prints the new string. Understanding this helps you write better code with strings in C#.