Questions: Variables and Assignment

Question 1

What is the value of x after these three lines execute? x = 10 y = x x = 20

• A. x is 10, y is 10
• B. x is 20, y is 20
• C. x is 20, y is 10
• D. x is 10, y is 20

Answer: (C)

After line 1, x holds 10. Line 2 copies the current value of x (which is 10) into y. Line 3 reassigns x to 20. Crucially, y still holds 10 — it captured the value at the time of assignment, not a live link to x. This tests the misconception that variables store expressions or references to other variables rather than evaluated values.

Question 2

In most programming languages, the statement x = x + 1 is a valid assignment.

• T. True
• F. False

Answer: True

In programming, = is the assignment operator, not a statement of mathematical equality. The right side (x + 1) is evaluated first using the current value of x, and the result is stored back into x. In math, x = x + 1 has no solution, which is why this confuses beginners who think of = as 'equals.'

Question 3

Explain why the order of assignment statements matters. Give a brief example.

Model answer: Assignment is sequential: each statement uses the current values of variables at that moment. For example, 'a = 5; b = a + 1; a = 0' results in b = 6 and a = 0, not b = 1, because b was assigned before a changed.

Variables hold snapshots, not formulas. Each assignment reads the current state, computes a value, and writes it. Reordering assignments can produce completely different results because the state changes between lines.