ITPEC FE Subject B October 2025 Question 4

The algorithm extracts digits from right to left using mod 10, then builds the reversed number by shifting the accumulator left (rev × 10) and adding each extracted digit.

• •A: `temp > 0` — the loop must check temp, not num, because temp is the variable being reduced each iteration. Using num > 0 would create an infinite loop since num never changes.
• •B: `rev × 10 + rm` — shifts existing reversed digits left by one decimal place and appends the current digit (rm). This is the standard "build a number digit by digit" pattern.
• •C: `integer part of (temp ÷ 10)` — removes the last digit from temp (integer division by 10).

Why not others:
- a-d) use num > 0 as the loop condition, but num is never modified → infinite loop
- e) and f) use rm × 10 + rev which reverses the addition order — would produce wrong results (e.g., for 456: first iteration gives 6×10+0=60 instead of 0×10+6=6)
- f) and h) use temp - rm for C, which doesn't properly remove the last digit (456-6=450, not 45)

Key rule: To reverse a number: extract last digit with mod 10, accumulate with rev × 10 + digit, remove last digit with integer part of (n ÷ 10).

AI-generated — may contain errors