Decisions Practice

These questions follow Making Decisions. A decision in code is a question with exactly one answer acted on — and most of the trouble comes from the values sitting right on the boundary between two branches.

Reading

1. Predict the output for mark = 70, then for mark = 69, then for mark = 80.

   if mark >= 80:
       print("Excellent")
   elif mark >= 70:
       print("Good")
   elif mark >= 50:
       print("Pass")
   else:
       print("Not yet")

2. What does this print when temperature is exactly 30?

   temperature = 30
   if temperature > 30:
       print("Open the windows.")
   print("done")

3. Find the fault and say which of the three kinds of error it is.

   days_late = 3
   if days_late > 0:
   print("Overdue")

4. Trace it. What prints when minutes is 0?

   if minutes > 0:
       if minutes < 30:
           print("Short session")
       else:
           print("Full session")
   else:
       print("Day off")

Writing

5. Write the three-tier version of an overdue message: 0 or fewer days is on time, up to 7 days gets a reminder, anything more gets a letter home. Test it with 0, 7, and 8.
6. A club meets only if at least five members are present and the room is booked. Write it with nested if statements, and print a different message for each of the three outcomes.
7. Somebody writes if mark = 80: and Python refuses to run the file at all. Why, and what did they mean?
8. Challenge. For the code in question 1, which four values of mark would you test to be confident every branch works, and why those four?

Answers

Answer 1

70 prints Good, 69 prints Pass, 80 prints Excellent. Python tries each condition in order and stops at the first True. >= includes the boundary value itself, which is why 70 is Good and not Pass.

Answer 2

Only done. 30 > 30 is False, so the indented line is skipped entirely. The unindented print is not part of the if and always runs. If 30 should count as hot, the condition needs >=.

Answer 3

The print is not indented, so Python never sees a body for the if:

IndentationError: expected an indented block after 'if' statement on line 2

It is a syntax error — the file never runs at all. Indent the print by four spaces and it works.

Answer 4

Day off. 0 > 0 is False, so Python jumps straight to the matching else and never looks at the inner if at all. Indentation is what pairs that else with the outer question rather than the inner one.

Answer 5

answer = input("Days late: ")
days_late = int(answer)
 
if days_late <= 0:
    print("On time.")
elif days_late <= 7:
    print("Just remind them.")
else:
    print("Send the letter home.")

0 gives On time., 7 gives Just remind them., and 8 gives Send the letter home. The middle branch needs no lower limit: it is only reached when the first condition already failed.

Answer 6

if members_present >= 5:
    if room_booked:
        print("Meeting goes ahead.")
    else:
        print("Enough people, but no room.")
else:
    print("Not enough people.")

With members_present = 4 this prints Not enough people. whether or not the room is booked — the inner question is never reached. That is the nesting working correctly.

Answer 7

= assigns a value; == compares two values. if mark = 80: asks Python to store something in the middle of a question, and Python refuses:

SyntaxError: invalid syntax. Maybe you meant '==' or ':=' instead of '='?

They meant if mark == 80:. Being caught by the compiler is the best outcome available for this mistake.

Answer 8

One value per branch, chosen at the boundaries — 80, 70, 50, and 49. The first three land exactly on a cutoff and prove that >= includes it; the 49 proves the else is reachable. Testing 80 matters far more than testing 83: bugs live at the edges, where > and >= disagree, and a value in the middle of a range cannot tell the two apart.