Left shift and right shift in C - Step-by-Step Execution

Concept Flow - Left shift and right shift

Start with number x

↓

Apply left shift x << n

↓

Multiply x by 2^n

↓

Apply right shift x >> n

↓

Divide x by 2^n (floor)

↓

End with new value

Start with a number, shift bits left to multiply by powers of two, shift bits right to divide by powers of two, then get the new value.

Execution Sample

C

int x = 4;
int left = x << 1;
int right = x >> 1;
printf("%d %d", left, right);

This code shifts 4 left by 1 (multiply by 2) and right by 1 (divide by 2), then prints the results.

Execution Table

Step	Operation	Value Before	Shift Amount	Value After	Explanation
1	Initialize x	N/A	N/A	4	Start with x = 4
2	Left shift x << 1	4 (binary 0100)	1	8 (binary 1000)	Shifts bits left by 1, multiplies by 2
3	Right shift x >> 1	4 (binary 0100)	1	2 (binary 0010)	Shifts bits right by 1, divides by 2 (floor)
4	Print results	N/A	N/A	8 2	Outputs left and right shift results

💡 All operations done, program ends after printing.

Variable Tracker

Variable	Start	After Left Shift	After Right Shift	Final
x	4	4	4	4
left	N/A	8	8	8
right	N/A	N/A	2	2

Key Moments - 3 Insights

Why does left shifting by 1 multiply the number by 2?

Because shifting bits left moves all bits one place higher, which doubles the value (see execution_table step 2).

Why does right shifting by 1 divide the number by 2 and round down?

Because shifting bits right moves bits one place lower, effectively dividing by 2 and dropping any remainder (see execution_table step 3).

Does the original variable x change after shifting?

No, shifting creates new values stored in separate variables (left and right), x remains unchanged (see variable_tracker).

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'left' after step 2?

A 4

B 8

C 2

D 16

💡 Hint

Check the 'Value After' column in step 2 of execution_table.

At which step does the value become 2 after shifting?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look for 'Value After' column where value is 2 in execution_table.

If we change x to 8, what would be the value of 'right' after right shift by 1?

A 16

B 8

C 4

D 2

💡 Hint

Right shift divides by 2, so half of 8 is 4 (see concept_flow and execution_table logic).

Concept Snapshot

Left shift (x << n) moves bits left n times, multiplying x by 2^n.
Right shift (x >> n) moves bits right n times, dividing x by 2^n (floor).
Original variable stays unchanged unless assigned.
Useful for fast multiplication/division by powers of two.
Shifts work on binary representation of numbers.

Full Transcript

This lesson shows how left and right bit shifts work in C. We start with a number x. Left shifting x by 1 moves bits left, doubling the number. Right shifting x by 1 moves bits right, halving the number and rounding down. The code example uses x=4, shifts left and right by 1, and prints results 8 and 2. Variables left and right hold shifted values; x stays 4. The execution table traces each step with values and explanations. Key points clarify why shifting multiplies or divides by powers of two and that original variables don't change unless reassigned. The quiz tests understanding of values after shifts and effects of changing x.