Checked and unchecked arithmetic in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Checked and unchecked arithmetic

Start Arithmetic Operation

↓

Is 'checked' context?

No→Perform unchecked operation

|Yes↓

Perform checked operation

↓

Overflow?

No→Return result

Yes↓

Throw OverflowException

The program decides if arithmetic is checked or unchecked. Checked operations detect overflow and throw an error; unchecked operations ignore overflow.

Execution Sample

C Sharp (C#)

int a = int.MaxValue;
int b = 1;
int c = checked(a + b);
int d = unchecked(a + b);

This code adds 1 to the maximum int value using checked and unchecked contexts to show overflow behavior.

Execution Table

Step	Operation	Context	Calculation	Overflow Detected	Result or Exception
1	a = int.MaxValue	N/A	a = 2147483647	No	a = 2147483647
2	b = 1	N/A	b = 1	No	b = 1
3	c = checked(a + b)	checked	2147483647 + 1	Yes	OverflowException thrown
4	d = unchecked(a + b)	unchecked	2147483647 + 1	Yes but ignored	-2147483648 (wrap around)

💡 Execution stops at step 3 due to OverflowException in checked context; unchecked continues with wrap-around.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
a	undefined	2147483647	2147483647	2147483647	2147483647
b	undefined	undefined	1	1	1
c	undefined	undefined	undefined	Exception	Exception
d	undefined	undefined	undefined	undefined	-2147483648

Key Moments - 2 Insights

Why does step 3 throw an OverflowException but step 4 does not?

Step 3 uses 'checked' context which detects overflow and throws an exception, as shown in execution_table row 3. Step 4 uses 'unchecked' context which ignores overflow and wraps the value, as shown in row 4.

What does 'unchecked' arithmetic do when overflow happens?

'Unchecked' arithmetic ignores overflow and wraps around the value to fit the data type, demonstrated in execution_table row 4 where the result becomes -2147483648.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of variable 'd' after step 4?

A OverflowException

B 2147483648

C -2147483648

D 2147483647

💡 Hint

Check the 'Result or Exception' column in row 4 of the execution_table.

At which step does the program throw an OverflowException?

A Step 3

B Step 2

C Step 4

D No exception thrown

💡 Hint

Look at the 'Overflow Detected' and 'Result or Exception' columns in the execution_table.

If we remove 'checked' from step 3, what would happen to variable 'c'?

A It would throw OverflowException

B It would wrap around like 'd'

C It would be zero

D It would be unchanged

💡 Hint

Compare the behavior of checked vs unchecked contexts in the execution_table rows 3 and 4.

Concept Snapshot

Checked and unchecked arithmetic in C# control overflow behavior.
Use 'checked' to detect overflow and throw exceptions.
Use 'unchecked' to ignore overflow and wrap values.
Default context depends on compiler settings.
Example: checked(a + b) throws if overflow occurs.
Unchecked allows silent wrap-around.

Full Transcript

This visual trace shows how C# handles arithmetic overflow using checked and unchecked contexts. Variables a and b are set to maximum int and 1. Adding them in a checked context causes an OverflowException at step 3. In an unchecked context at step 4, overflow is ignored and the result wraps around to -2147483648. The variable tracker shows values before and after each step. Key moments clarify why exceptions happen only in checked context and how unchecked wraps values. The quiz tests understanding of variable values and overflow behavior. The snapshot summarizes the key rules and syntax for checked and unchecked arithmetic.