In C, evaluate nested assignments and function calls: what does this program print for k?
#include
int func1(int);
int main()
{
int k = 35;
k = func1(k = func1(k = func1(k)));
printf("k=%d
", k);
return 0;
}
int func1(int k)
{
k++;
return k;
}
-
Ak=35
-
Bk=36
-
Ck=37
-
Dk=38
-
Ek=39
Answer
Correct Answer: k=39
Explanation
Introduction / Context:This classic C puzzle checks understanding of nested function calls, right-associative assignments, and the fact that assignment is an expression whose value is the assigned value. The helper function increments its argument and returns the incremented value.
Given Data / Assumptions:
- int func1(int k) { k++; return k; } increments and returns its input.
- Initial k = 35.
- Compound statement: k = func1( k = func1( k = func1(k) ) );
- Standard C semantics; each inner expression must be fully evaluated to supply the argument to the next call.
Concept / Approach:Work from the innermost parentheses outward. Each func1 call adds 1 to its argument and returns that value. Each k = ... not only stores into k but also yields that stored value, which then becomes the argument to the next outer call.
Step-by-Step Solution:Start k = 35.Innermost: func1(k) = 36; assign k = 36.Middle: need k = func1(k): with k = 36, func1(36) = 37; assign k = 37; the middle call is func1(37) = 38; then the middle assignment sets k = 38.Outer: evaluate func1(38) = 39; final outer assignment sets k = 39.Prints “k=39”.
Verification / Alternative check:Replace nested form with sequential statements to verify: k=func1(k); k=func1(k); k=func1(k); would give 38; however the given expression performs an extra func1 due to the outer call applied to the already-assigned middle result, hence 39.
Why Other Options Are Wrong:“k=38” overlooks that the outermost func1 runs after the middle assignment has already set k to 38. “k=35/36/37” ignore one or more increments.
Common Pitfalls:Forgetting that an assignment returns the assigned value; miscounting the number of func1 calls; assuming chained comparisons or left-to-right argument evaluation semantics that do not apply to nested expressions.
Final Answer:k=39