iGCSE Computer Science - Distance Learning

Tutor Marked Assignment 6
Tutor Marked Assignment 8 (Programming)

Negative Binary Numbers (2023 Specification Only)

New 2023 Syllabus Only

Negative numbers are a new topic for the iGCSE and won’t be seen in any of the past papers. That’s not a problem as this topic has been around in the A Level for many years so we have plenty of practice questions!

Even though this topic was an A Level topic, don’t worry too much about it being really difficult as there’s a simple trick to creating a negative binary number that will work every time!

Representing negative numbers in binary requires us to identify the sign that is used in front of the number. You will already be familiar with using a sign for negative numbers in maths as if the number is negative then a minus sign is placed before it. a signed integer is simply a whole number that is identified as either positive or negative and can be either.

Although it was explained in the video, the instructions below are a handy reference to how we create a negative number in Two’s Complement:

There are several ways in which to convert from denary into a negative Two’s Complement format. However, one particular way is very useful for the exam as it does not rely on a brute force technique and makes use of your prior understanding of how to create a positive binary number. Following the steps in the algorithm below we can transform a positive number into a negative number using the Two’s Complement method:

  • set up the columns with the most significant bit as a minus number
  • convert the positive version of the number into its fixed point binary format
  • identify the least significant one
  • retain the same numbers for the least significant one and any trailing zeros
  • flip all other digits towards the most significant figure
Twos Complement Binary

Of course, don’t trust me and just use my example! Take any negative integer and test this theory out for yourself.

Task

Now you’ve had a chance to try out your own numbers, download this practice sheet. The answers are on the second sheet, so you may want to hide this!