AND for masking bits in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this bit masking code?

Consider the following C code that uses the AND operator to mask bits. What will be printed?

Embedded C

unsigned char value = 0xAB;  // 10101011 in binary
unsigned char mask = 0x0F;   // 00001111 in binary
unsigned char result = value & mask;
printf("0x%X", result);

A 0x0B

B 0xAB

C 0xAF

D 0xA0

💡 Hint

AND operator keeps bits set only if both bits are 1.

The value 0xAB is 10101011 in binary. The mask 0x0F is 00001111. ANDing them keeps only the last 4 bits: 10101011 & 00001111 = 00001011 which is 0x0B.

❓ Predict Output

intermediate

What does this masking code output?

Given the code below, what is the printed output?

Embedded C

unsigned int flags = 0xF0F0;  // binary: 1111000011110000
unsigned int mask = 0x0FF0;  // binary: 0000111111110000
unsigned int masked = flags & mask;
printf("0x%X", masked);

A 0x00F0F0

B 0x00F0

C 0F00x0

D x00F0

💡 Hint

AND keeps bits where both are 1.

flags = 0xF0F0 (1111000011110000), mask = 0x0FF0 (0000111111110000). ANDing gives 0000000011110000 = 0x00F0.

❓ Predict Output

advanced

What is the output of this masking with shifting?

What will this C code print?

Embedded C

unsigned char data = 0x5A;  // 01011010
unsigned char mask = 0x03;  // 00000011
unsigned char result = (data >> 2) & mask;
printf("%u", result);

A 1

B 3

C 2

D 0

💡 Hint

Shift right first, then mask with 0x03.

data >> 2 shifts 01011010 to 00010110 (decimal 22). Mask 0x03 is 00000011. 00010110 & 00000011 = 00000010 = 2.

❓ Predict Output

advanced

What is the output of this combined mask?

What does this code print?

Embedded C

unsigned int x = 0x12345678;
unsigned int mask = 0x00FF00FF;
unsigned int result = x & mask;
printf("0x%X", result);

A 0x00340078

B 0x12005678

C 0x12340000

D 0x00345600

💡 Hint

AND keeps bits where mask bits are 1.

x = 0x12345678, mask = 0x00FF00FF. ANDing keeps bytes 2 and 0: 0x00340078.

❓ Predict Output

expert

What is the output of this bit masking with signed integer?

Consider this code snippet. What will it print?

Embedded C

int x = -42;  // Two's complement representation
unsigned int mask = 0xFF;
unsigned int result = x & mask;
printf("0x%X", result);

A 0xFFFFFF2A

B 0x2A

C 0xFFFFFFD6

D 0xD6

💡 Hint

Masking with 0xFF keeps the lowest 8 bits.

-42 in two's complement (32-bit) is 0xFFFFFFD6. AND with 0xFF keeps 0xD6 (214 decimal).