GCSE · Computer Science · AQA · Spec 8525

Not equal to (relational operator)

Picture a lock screen asking one question about your PIN: is it different from the real one? Yes, it stays locked. No, you're in. That question is !=.

Computer Science · Programming

One question, three different paths

The secret number is 10. Step through three runs of the same code and watch what guess != 10 answers each time.

Before you step through run 2: when the player types 10, which message do you think gets printed?

 1  guess = int(input("Your guess: "))
 2  if guess > 10:
 3      print("Too high")
 4  elif guess != 10:
 5      print("Too low")
 6  else:
 7      print("Spot on!")

Variables

guess=7

Output

Your guess: 7

Step 1: Run 1. The player types 7, so guess now holds 7.

1 / 12

Press Next to move one line at a time. Watch which line lights up after each question is answered.

Step 1 of 12: Run 1. The player types 7, so guess now holds 7..

Your turn

True or False?

Pick a comparison, then drop it into the answer it evaluates to.

Still to sort

Evaluates to True (0)

The two values are different.

Where the line is: Any difference at all counts. Being close (49 and 50) is still different.

Evaluates to False (0)

The two values are exactly the same.

Where the line is: Work out each side first. If both sides come to the same value, != gives False.

6 of 6 still to sort.

No program this time, just the comparisons. Commit to an answer for each one, then read why.

One symbol, three jobs

=, == or !=?

A game runs the line lives = 3. Later it checks two conditions: lives == 3 and lives != 0.

Which of these is closest to what you think is going on?

lives = 3 stores 3 in lives. The other two only ask questions, and both come out True.All three check lives against a number. = and == are just two ways of writing 'equals'.lives != 0 makes sure lives isn't 0, by changing it if it needs to.lives != 0 is False, because != only gives True when the two values match.

How sure are you?

I'm sureI think soI'm guessing

lives = 3 stores 3 in lives. The other two only ask questions, and both come out True.

This matches the evidence

Spot on. A single = is assignment: it puts a value into a variable and asks nothing. == asks 'is lives the same as 3?' (yes, True) and != asks 'is lives different from 0?' (yes, True). Neither question changes lives.

All three check lives against a number. = and == are just two ways of writing 'equals'.

This is a common misconception

This is the big one to fix. In Python a single = never compares. It's assignment: lives = 3 puts 3 into lives. To ask whether two values are the same you need two equals signs, ==. To ask whether they're different, !=.

lives != 0 makes sure lives isn't 0, by changing it if it needs to.

This is a common misconception

A comparison never changes a value. lives != 0 just looks at lives, compares it with 0 and answers True or False. If you want to change lives, that's a job for assignment with a single =.

lives != 0 is False, because != only gives True when the two values match.

This is a common misconception

That's the meaning flipped round. != asks 'are they different?' lives holds 3, and 3 is different from 0, so the answer is yes: True. When the values match, != gives False.

= stores. == asks 'the same?'. != asks 'different?'. These are Python's symbols; other programming languages may write these operators with different symbols.

Spot the bug

Why is there no warning?

This program should print a warning whenever total is not equal to 100. A student sets total to 80 to test it, and the warning doesn't appear. Which line is wrong?

A student's program — which line goes wrong?

total = 80
if total == 100:
print("Warning: the total must be 100")
else:
print("Total accepted")

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

A question your program asks: are these two values different? The answer is always True or False, and that answer picks the path.

What you need to know

Say what a relational operator does and what a condition evaluates to.
Read != as 'not equal to' and evaluate a != comparison to True or False.
Tell != apart from == (equal to) and from a single = (assignment).
Name the six relational operators: ==, !=, <, <=, > and >=.
Write a != condition from an English statement, such as 'total is not equal to 100'.
Follow which branch of an if / elif / else runs when a condition uses !=.

The big picture

A relational operator compares two values, and the comparison (a condition) evaluates to either True or False. Not equal to, written != in Python, asks whether two values are different: it gives True when they differ and False when they're the same. It's the opposite of ==, which asks whether two values are equal, and neither should be confused with a single =, which is assignment. As the condition of an if / elif / else, a != comparison helps decide which branch runs: the first condition to evaluate to True wins.

Key points

1A relational operator compares two values. The comparison, called a condition, always evaluates to True or False.

2!= means 'not equal to'. It asks 'are these two values different?', so total != 1 reads 'does total not equal 1?'.

3!= gives True when the two values are different and False when they're the same.

4!= is the opposite of ==, which asks whether two values are equal. A single = isn't a comparison at all: it's assignment. Other languages may use different symbols for these operators.

5The six relational operators are ==, !=, <, <=, > and >=.

6In an if / elif / else, the branch whose condition is the first to evaluate to True is the one that runs.

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Worked example

Problem

A vending machine stores the amount paid, in pence, in a variable called paid. Write an if / else that prints "Please pay 150p" when paid is not equal to 150 and "Thank you" otherwise. Then say what it prints when paid is 150, and when paid is 200.

⚠ Watch out

Writing a single = in a condition, as in if total = 100:. A single = is assignment: it stores a value rather than comparing. To ask 'the same?' use ==, and to ask 'different?' use !=.

🧠

Memory hook

Read the ! as 'not': != is 'not equal'. Then ask it out loud: 'Different?' Yes means True. No means False.

✓

Check yourself

x holds 6. What do x != 6 and x != 9 evaluate to? (x != 6 is False: the values match. x != 9 is True: 6 and 9 are different.)

Flashcards

(13)

What does a relational operator do?

It compares two values. The comparison (a condition) evaluates to True or False.

What does != mean?

Not equal to. It asks: are these two values different?

How is 'not equal to' written in Python?

An exclamation mark followed by an equals sign: !=

When does a != comparison evaluate to True?

When the two values are different.

What does a != comparison give when both values are the same?

False. They aren't different, so the answer to 'not equal?' is no.

What does == check?

Whether one value is equal to another. It's the equal to comparison.

What does a single = do in Python?

Assignment: it stores a value in a variable. It doesn't compare anything.

How are == and != related?

They're opposites. Compare any two values and exactly one of them is True.

Name the six relational operators.

== (equal to), != (not equal to), < (less than), <= (less than or equal to), > (greater than), >= (greater than or equal to).

Write 'total is not equal to 100' as code.

total != 100

In an if / elif / else, which branch runs?

The one whose condition is the first to evaluate to True. If none is True, the else branch runs.

Does a comparison like score != 0 change score?

No. It only reads the value and gives True or False. Only assignment changes a variable.

Does every programming language write 'not equal to' as != ?

Not necessarily. Other languages may use different symbols for their relational operators.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Not equal to (relational operator)

One question, three different paths

True or False?

Six relational operators

=, == or !=?

Why is there no warning?

More AQA GCSE Computer Science topics