Variables and Expressions Practice

These questions follow Data in Programs — the tracing habit comes from Predict the Output. Trace on paper first; the computer checks.

Questions

1. After these lines run, what is stored in score? Explain why = here cannot mean what it means in maths class.

   score = 10
   score = score + 5

2. Predict the output, character by character — spaces count.

   first = "Rob"
   last = "Ott"
   print(first + last)

3. Predict the output. Does changing a afterwards change b?

   a = 3
   b = a
   a = 7
   print(b)

4. Find the bug. prize = "100" then total = prize + 50 — and line 2 crashes. Name the problem, then fix it two different ways.
5. Write a three-line snippet: your name in one variable, your favourite number in another, then print a sentence using both.
6. Challenge. Variables red and blue hold values. Swap them — afterwards, each must hold the other’s old value.
7. Data types. State the data type (int, float, str, or bool) of each: (a) 42, (b) 3.14, (c) "True", (d) True, (e) "0". Explain why type("True") is different from type(True) and how each is used in a program.
8. Order of operations. Determine the exact value of each expression, showing the evaluation order: (a) 10 + 4 * 2 ** 3, (b) (10 + 4) * 2 ** 3, (c) 20 - 6 // 2 + 5 % 2. Explain why parentheses are required when calculating an average (a + b) / 2.

Answers

Answer 1

score is 15. In Python, = is an instruction — work out the right side, store it on the left — so line 2 adds 5 to what is there.

Answer 2

RobOtt — no space, because + glues strings together exactly as they are. Want Rob Ott? Add it yourself: first + " " + last.

Answer 3

It prints 3. Line 2 copies the value 3 into b — it does not tie b to a forever. Reassigning a later changes nothing.

Answer 4

prize holds the text "100", and adding text to a number is a TypeError. Fix 1: prize = 100. Fix 2: total = int(prize) + 50.

Answer 5

One version — yours will differ: name = "Priya", number = 17, then print(name + " picks " + str(number) + " every time.").

Answer 6

A third variable holds one value while the other moves: spare = red, red = blue, blue = spare. Try it without the spare and watch a value get overwritten — that is why it exists.

Answer 7

(a) int (integer), (b) float (decimal floating-point number), (c) str (text string), (d) bool (Boolean truth value), (e) str (text string, because quotes surround it). "True" is text for printing or matching words; True is a boolean truth value used directly in conditionals (if True:) to decide execution flow.

Answer 8

(a) 42 — exponent first ($2^3=8$), then multiply ($4\times 8=32$), then add ($10+32=42$). (b) 112 — brackets first ($10+4=14$), exponent ($2^3=8$), then multiply ($14\times 8=112$). (c) 18 — division ($6//2=3$) and modulo ($5\%2=1$), then left-to-right ($20-3+1=18$). Without brackets in a + b / 2, division outranks addition, dividing only b by 2 rather than the sum.

Curriculum connection

C1.3

identify various types of data and explain how they are used within programs

Link to original

C1.4

determine the appropriate expressions and instructions to use in a programming statement, taking into account the order of operations

Link to original

C2.1

use variables, constants, expressions, and assignment statements to store and manipulate numbers and text in a program

Link to original