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Programming Basics (Pseudocode Tracing)

⊕ is bitwise exclusive OR. What are the values of x and y after the following program runs?

integer: x ← 12, y ← 10
x ← x ⊕ y
y ← x ⊕ y
x ← x ⊕ y
  1. Ax = 10, y = 12
  2. Bx = 6, y = 12
  3. Cx = 12, y = 10
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Answer: A. x = 10, y = 12

In binary, 12 = 1100 and 10 = 1010. The first assignment gives x = 1100 ⊕ 1010 = 0110 = 6, the second y = 0110 ⊕ 1010 = 1100 = 12, and the third x = 0110 ⊕ 1100 = 1010 = 10. This swaps the values without a temporary variable, using the fact that XOR with the same value twice restores the original (a ⊕ b ⊕ b = a).

  • A. Correct. Three exclusive ORs swap x and y.
  • B. These are the values after the second assignment.
  • C. This assumes the values are unchanged. They are actually swapped.
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