Left shift and right shift in C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the left shift operator (<<) do in C?

It moves the bits of a number to the left by a specified number of positions, effectively multiplying the number by 2 for each shift.

beginner

What is the effect of the right shift operator (>>) in C?

It moves the bits of a number to the right by a specified number of positions, effectively dividing the number by 2 for each shift (for unsigned numbers).

beginner

Explain what happens when you do: int x = 4; int y = x << 1;

The value of x (4) is shifted left by 1 bit, which multiplies it by 2. So y becomes 8.

intermediate

What is a potential risk when using left shift on signed integers?

Shifting bits into the sign bit can cause undefined behavior or unexpected negative values.

intermediate

How does right shift behave differently for signed and unsigned integers in C?

For unsigned integers, right shift fills with zeros (logical shift). For signed integers, it may fill with the sign bit (arithmetic shift), preserving the sign.

What is the result of 3 << 2 in C?

A 12

B 6

C 1

D 8

3 in binary is 00000011. Shifting left by 2 bits gives 00001100, which is 12.

What does the right shift operator (>>) do to the bits of an unsigned integer?

A Fills left bits with zeros

B Fills left bits with ones

C Reverses the bits

D Swaps the bits

Right shift on unsigned integers fills the left bits with zeros (logical shift).

Which operator would you use to multiply an integer by 8 using bit shifts?

A << 2

B >> 3

C << 3

D >> 2

Shifting left by 3 bits multiplies the number by 2^3 = 8.

What happens if you left shift a signed integer into its sign bit?

A No change

B Always zero

C Always positive

D Undefined behavior or negative value

Shifting into the sign bit can cause undefined behavior or change the sign unexpectedly.

If int x = -16; what might x >> 2 do?

A Divide by 4 and fill with zeros

B Divide by 4 and keep the sign

C Multiply by 4

D Cause a compile error

Right shift on signed integers usually performs arithmetic shift, preserving the sign.

Explain how left shift and right shift operators work in C and give a simple example for each.

Think about how shifting bits changes the number's value.

What are the differences in behavior of right shift on signed versus unsigned integers in C?

Consider how negative numbers are handled.