Signed vs unsigned behavior on 8-bit MCU in Embedded C - Quick Revision & Key Differences

Recall & Review

beginner

What is the difference between signed and unsigned integers on an 8-bit MCU?

Signed integers can represent both positive and negative numbers, while unsigned integers represent only non-negative numbers (zero and positive). On an 8-bit MCU, signed integers typically use one bit for the sign, reducing the maximum positive value.

beginner

What is the range of an 8-bit signed integer?

An 8-bit signed integer ranges from -128 to 127. This is because one bit is used for the sign, and the remaining 7 bits represent the value.

beginner

What is the range of an 8-bit unsigned integer?

An 8-bit unsigned integer ranges from 0 to 255. All 8 bits are used to represent the value, so no bits are reserved for sign.

intermediate

What happens when you assign a negative value to an unsigned 8-bit variable on an MCU?

The negative value wraps around due to underflow, resulting in a large positive number. For example, assigning -1 to an unsigned 8-bit variable results in 255.

intermediate

How does overflow behave differently for signed and unsigned 8-bit integers?

For unsigned integers, overflow wraps around from the maximum value back to zero. For signed integers, overflow causes undefined behavior or wraps around in two's complement form, which can lead to negative values.

What is the maximum value of an 8-bit unsigned integer?

A 128

B 127

C 255

D 256

An 8-bit unsigned integer uses all 8 bits for value, so max is 2^8 - 1 = 255.

What is the range of an 8-bit signed integer?

A -128 to 127

B -256 to 255

C -127 to 128

D 0 to 255

Signed 8-bit integers use one bit for sign, so range is -128 to 127.

What happens if you assign -1 to an unsigned 8-bit variable?

A It stores 255

B It stores -1

C It causes an error

D It stores 0

Unsigned variables wrap around, so -1 becomes 255.

Which of these is true about overflow in unsigned 8-bit integers?

A It stays at max value

B It causes program crash

C It becomes negative

D It wraps around to zero

Unsigned overflow wraps around to zero due to modulo arithmetic.

Why is one bit reserved in signed 8-bit integers?

A To store parity

B To store the sign (positive or negative)

C To increase range

D To store overflow info

One bit is used to indicate if the number is positive or negative.

Explain the difference between signed and unsigned integers on an 8-bit MCU and how their ranges differ.

Think about how many values can be represented with 8 bits and how sign affects that.

Describe what happens when you assign a negative number to an unsigned 8-bit variable on an MCU.

Consider how unsigned variables handle values outside their range.