Lesson Plan

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Lesson Plan
Grade: Date: 17/01/2026
Subject: Computer Science
Lesson Topic: Use the two’s complement number system to represent positive and negative 8-bit binary integers
Learning Objective/s:
  • Describe the range of values representable by an 8‑bit two’s complement integer.
  • Explain the step‑by‑step process for converting positive and negative decimal numbers to 8‑bit two’s complement binary.
  • Apply the conversion method to solve practice problems and interpret given 8‑bit patterns.
  • Analyse common errors such as missing padding or incorrect bit inversion and correct them.
Materials Needed:
  • Projector and screen
  • Whiteboard and markers
  • Worksheets with conversion tables and practice exercises
  • Calculators (binary mode) or laptops with a simple conversion app
  • Printed handouts of examples and common mistakes
 Introduction:

Begin by asking students how they would represent “‑5” using only 0s and 1s. Recall their knowledge of binary for positive numbers and introduce the need for a unified system for signed values. Explain that by the end of the lesson they will be able to convert any decimal integer between –128 and 127 into an 8‑bit two’s complement binary pattern and back.
Lesson Structure:
  1. Do‑Now (5'): Students write the 8‑bit binary of 23 on mini‑whiteboards; quick peer check.
  2. Mini‑lecture (10'): Explain two’s complement, sign bit, range (‑128 to 127) using projector slides.
  3. Guided practice (15'): Demonstrate conversion of +45 and –45 step‑by‑step (binary, padding, invert, add 1).
  4. Pair activity (15'): Complete worksheet converting +23, –23, +85, –85, +0 and the trick “‑0”. Teacher circulates to provide feedback.
  5. Quick check (5'): Present binary 11101010; class decodes the decimal value and justifies the answer.
  6. Common‑mistake review (5'): Show flawed examples (missing padding, wrong order of invert/add) and have students correct them.
  7. Exit ticket (5'): Each student writes one essential step for correct conversion and one common error to avoid.
Conclusion:

Summarise the three‑step rule for negative numbers (write positive binary, invert bits, add 1) and remind students of the importance of 8‑bit padding. Collect exit tickets to gauge understanding, and assign a homework worksheet that includes additional numbers and a few decoding challenges.