Programming and Data Structures · Recursion
Official IIT answer key · IIT Kanpur · Audited Aug 2026
GATE CSE 2023 Q47 · MCQ · 2 marks
foo and the binary tree shown.
typedef struct node {
int val;
struct node *left, *right;
} node;
int foo(node *p) {
int retval;
if (p == NULL)
return 0;
else {
retval = p->val + foo(p->left) + foo(p->right);
printf("%d ", retval);
return retval;
}
}
When foo is called with a pointer to the root node of the given binary tree, what will it print?
Key concept
Topic notes
GATE tests Recursion primarily through direct execution tracing of recursive C code snippets, stack-unwinding behavior (pre-order vs. post-order execution), and termination/infinite recursion analysis. Questions frequently incorporate static variables, pointer/reference aliasing, mutual recursion, and tree/array traversals to test whether candidates can systematically maintain call frames. In recent years, the focus has expanded from standard tracing to higher-order mathematical characterizations (e.g., finding the smallest input or maximum output value of composed recurrences).
Full Recursion guide →Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.