Left shift and right shift in C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to left shift the number 1 by 3 positions.

C

int result = 1 [1] 3;
printf("%d\n", result);

Drag options to blanks, or click blank then click option'

A<<

B>>

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using the right shift operator instead of left shift.

Using arithmetic operators like + or -.

The left shift operator << moves bits to the left, multiplying the number by 2 for each shift.

2fill in blank

medium

Complete the code to right shift the number 16 by 2 positions.

C

int result = 16 [1] 2;
printf("%d\n", result);

Drag options to blanks, or click blank then click option'

A>>

B<<

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using the left shift operator instead of right shift.

Using arithmetic operators like + or -.

The right shift operator >> moves bits to the right, dividing the number by 2 for each shift.

3fill in blank

hard

Fix the error in the code to correctly left shift the variable x by 4.

C

int x = 2;
int y = x [1] 4;
printf("%d\n", y);

Drag options to blanks, or click blank then click option'

A>>

B<<

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using right shift operator instead of left shift.

Using arithmetic operators.

To left shift the value of x by 4 bits, use the << operator.

4fill in blank

hard

Fill both blanks to create a dictionary-like structure using bit shifts: shift 1 left by 5 and shift 32 right by 3.

C

int a = 1 [1] 5;
int b = 32 [2] 3;
printf("%d %d\n", a, b);

Drag options to blanks, or click blank then click option'

A<<

B>>

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong shift operators.

Using arithmetic operators instead of shifts.

Use left shift << to multiply by powers of two, and right shift >> to divide by powers of two.

5fill in blank

hard

Fill all three blanks to compute: shift x left by 2, y right by 1, and add z.

C

int x = 3, y = 8, z = 5;
int result = (x [1] 2) + (y [2] 1) + [3];
printf("%d\n", result);

Drag options to blanks, or click blank then click option'

A<<

B>>

Cz

Dy

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up shift operators.

Adding wrong variables.

Shift x left by 2 bits, shift y right by 1 bit, then add z.

Practice

1. What does the left shift operator << do to an integer in C?

easy

A. Moves bits to the left, multiplying the number by powers of two

B. Moves bits to the right, dividing the number by powers of two

C. Reverses the bits of the number

D. Sets all bits to zero

Solution

1. Step 1: Understand left shift operation

   The left shift operator moves all bits in the number to the left by the specified count.

2. Step 2: Effect on the number's value

   Each left shift multiplies the number by 2, so shifting left by n multiplies by 2^n.

3. Final Answer:

   Moves bits to the left, multiplying the number by powers of two -> Option A

4. Quick Check:

   Left shift = multiply by 2^n [OK]

Hint: Left shift multiplies by 2 to the power of shift count [OK]

Common Mistakes:

• Confusing left shift with right shift
• Thinking left shift divides the number
• Assuming left shift reverses bits

2. Which of the following is the correct syntax to shift the integer variable x right by 3 bits in C?

easy

A. x >>> 3;

B. x >> 3;

C. x << 3;

D. x >>3

Solution

1. Step 1: Identify the right shift operator in C

   The right shift operator is >> and requires spaces or no spaces around it.

2. Step 2: Check syntax correctness

   x >> 3; is correct syntax. x << 3; is left shift, x >>> 3; is invalid in C, and x >>3 is missing a semicolon.

3. Final Answer:

   x >> 3; -> Option B

4. Quick Check:

   Right shift syntax = x >> n; [OK]

Hint: Right shift uses >> with semicolon to end statement [OK]

Common Mistakes:

• Using >>> which is not valid in C
• Confusing left shift << with right shift >>
• Omitting semicolon at end

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

int x = 4;
int y = x << 2;
printf("%d", y);

medium

A. 0

B. 1

C. 8

D. 16

Solution

1. Step 1: Understand the initial value of x

   x is 4, which in binary is 00000100.

2. Step 2: Apply left shift by 2 bits

   Shifting left by 2 bits multiplies 4 by 2^2 = 4 * 4 = 16.

3. Final Answer:

   16 -> Option D

4. Quick Check:

   4 << 2 = 16 [OK]

Hint: Left shift by n multiplies by 2^n [OK]

Common Mistakes:

• Calculating 4 << 2 as 8 instead of 16
• Confusing left shift with right shift
• Ignoring the shift count

4. Find the error in this C code snippet:

int a = 32;
int b = a >> 2
printf("%d", b);

medium

A. Wrong operator used for right shift

B. Incorrect printf format specifier

C. Missing semicolon after right shift operation

D. Variable b is not declared

Solution

1. Step 1: Check syntax line by line

   The line int b = a >> 2 is missing a semicolon at the end.

2. Step 2: Verify other parts

   The operator >> is correct, printf uses %d for int, and b is declared properly.

3. Final Answer:

   Missing semicolon after right shift operation -> Option C

4. Quick Check:

   Every statement needs semicolon [OK]

Hint: Check for missing semicolons after shift operations [OK]

Common Mistakes:

• Assuming >> is invalid operator
• Thinking printf format is wrong
• Ignoring missing semicolon errors

5. Given int x = 1;, what is the value of y after this operation?

int y = (x << 3) >> 1;

hard

A. 4

B. 8

C. 16

D. 2

Solution

1. Step 1: Calculate left shift (x << 3)

   Left shifting 1 by 3 bits multiplies 1 by 2^3 = 8.

2. Step 2: Calculate right shift of result by 1

   Right shifting 8 by 1 bit divides 8 by 2^1 = 2, so 8 / 2 = 4.

3. Final Answer:

   4 -> Option A

4. Quick Check:

   (1 << 3) >> 1 = 8 >> 1 = 4 [OK]

Hint: Left shift then right shift: multiply then divide by powers of two [OK]

Common Mistakes:

• Calculating (1 << 3) as 16
• Ignoring right shift effect
• Mixing up shift directions