Left shift and right shift behavior in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of left shift on unsigned integer

What is the output of this C code snippet when compiled and run on a typical 32-bit system?

Embedded C

unsigned int x = 1;
unsigned int y = x << 3;
printf("%u", y);

A 8

B 16

C 0

D 1

💡 Hint

Left shifting by 3 bits multiplies the number by 2^3.

Left shifting 1 by 3 bits moves the bit pattern 3 places to the left, resulting in 8.

❓ Predict Output

intermediate

Right shift on signed negative integer

What is the output of this C code snippet on a system where right shift of signed integers is arithmetic?

Embedded C

int x = -16;
int y = x >> 2;
printf("%d", y);

A 0

B 1073741820

C -1

D -4

💡 Hint

Right shift on signed negative integers usually fills with sign bit (arithmetic shift).

Arithmetic right shift divides by powers of two rounding toward negative infinity, so -16 >> 2 is -4.

❓ Predict Output

advanced

Behavior of left shift causing overflow

What is the output of this C code snippet on a 32-bit unsigned integer?

Embedded C

unsigned int x = 0x80000000;
unsigned int y = x << 1;
printf("%u", y);

A 4294967295

B 0

C 2147483648

D 1

💡 Hint

Left shifting the highest bit moves it out of the 32-bit range.

Shifting 0x80000000 left by 1 bit discards the highest bit, resulting in 0.

❓ Predict Output

advanced

Right shift on unsigned integer with large shift count

What is the output of this C code snippet on a 32-bit unsigned integer?

Embedded C

unsigned int x = 1;
unsigned int y = x >> 33;
printf("%u", y);

A 0

B 1

C Undefined behavior

D 2

💡 Hint

Shifting by more than or equal to the bit width results in zero for unsigned types.

Right shifting 1 by 33 bits on a 32-bit unsigned integer results in 0 because bits shifted out are lost.

🧠 Conceptual

expert

Difference between logical and arithmetic right shift

Which statement correctly describes the difference between logical and arithmetic right shift in C?

A Logical right shift fills with zeros; arithmetic right shift fills with the sign bit.

B Logical right shift fills with the sign bit; arithmetic right shift fills with zeros.

C Both logical and arithmetic right shifts fill with zeros regardless of sign.

D Both logical and arithmetic right shifts fill with the sign bit regardless of sign.

💡 Hint

Think about how negative numbers behave when shifted right.

Logical right shift always fills with zeros; arithmetic right shift preserves the sign by filling with the sign bit.