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The following function justDoIt() is a part of some class. Assume num is a positive integer. public…
The following function justDoIt() is a part of some class. Assume num is a positive integer.
public int justDoIt(int num)
{
if (num == 0)
return 0;
int c = justDoIt(num / 2);
int bit = num % 2;
System.out.print(bit);
return c + (bit == 1 ? 1 : 0);
}(a)[2.0]
What will the function justDoIt( ) return when num = 126?
(b)[1.0]
What is the function justDoIt( ) performing apart from recursion?
Answer
Answer (a)
AIDry run of justDoIt(126) (verified by running the code):
justDoIt(126) → calls justDoIt(63); bit=126%2=0 → prints '0'
justDoIt(63) → calls justDoIt(31); bit=63%2=1 → prints '1'
justDoIt(31) → calls justDoIt(15); bit=31%2=1 → prints '1'
justDoIt(15) → calls justDoIt(7); bit=15%2=1 → prints '1'
justDoIt(7) → calls justDoIt(3); bit=7%2=1 → prints '1'
justDoIt(3) → calls justDoIt(1); bit=3%2=1 → prints '1'
justDoIt(1) → calls justDoIt(0); bit=1%2=1 → prints '1'
justDoIt(0) → returns 0 (base case)
As the calls unwind, the bits print in order: 1111110 (this is 126 written in binary), and the count c accumulates 1 for every bit equal to 1 — there are six 1's among the seven bits.
Return value: 6
Answer (b)
AIApart from recursion, the function displays (prints) the binary equivalent of num, one bit at a time from the most significant bit to the least significant bit, and it counts and returns the number of 1's (set bits) present in that binary representation.
From ISC 2026 Improvement Computer Science Paper 1, question 2(iii).