Call stack behavior - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this recursive function?

Consider the following C code that uses recursion. What will it print when run?

C

#include <stdio.h>

void printNumbers(int n) {
    if (n == 0) return;
    printNumbers(n - 1);
    printf("%d ", n);
}

int main() {
    printNumbers(3);
    return 0;
}

A 3 2 1

B 1 2 3

C 0 1 2 3

D 3 2 1 0

💡 Hint

Think about when the printf statement runs during the recursion.

The function calls itself with n-1 before printing. So it prints numbers in ascending order after reaching the base case.

❓ Predict Output

intermediate

What is the output of nested function calls?

Analyze the output of this C program with nested function calls.

C

#include <stdio.h>

void f1() {
    printf("A");
}

void f2() {
    printf("B");
    f1();
    printf("C");
}

int main() {
    f2();
    return 0;
}

A CAB

B ABC

C BCA

D BAC

💡 Hint

Follow the order of function calls and prints carefully.

f2 prints 'B', calls f1 which prints 'A', then f2 prints 'C'. So output is 'BAC'.

🔧 Debug

advanced

What error occurs in this recursive function?

Examine this recursive function. What error will it cause when run?

C

#include <stdio.h>

void recurse(int n) {
    printf("%d ", n);
    recurse(n + 1);
}

int main() {
    recurse(1);
    return 0;
}

A Stack overflow (infinite recursion)

B Segmentation fault due to null pointer

C Compilation error: missing return type

D No error, prints numbers from 1 to 10

💡 Hint

Consider what happens when the function never stops calling itself.

The function calls itself without a base case, causing infinite recursion and stack overflow.

📝 Syntax

advanced

Which option causes a stack corruption due to wrong function pointer usage?

Identify which code snippet will cause stack corruption because of incorrect function pointer usage.

A void (*fp)() = (void (*)())1234; fp();

B void (*fp)() = &main; fp();

C void (*fp)() = NULL; if(fp) fp();

D void (*fp)() = &printf; fp();

💡 Hint

Think about what happens when you call a function pointer set to an invalid address.

Option A sets a function pointer to an invalid address (1234) and calls it, causing stack corruption or crash.

🚀 Application

expert

How many stack frames are active at the deepest point?

Given this recursive function, how many stack frames exist at the deepest recursion call?

C

#include <stdio.h>

void countDown(int n) {
    if (n == 0) return;
    countDown(n - 1);
    printf("%d ", n);
}

int main() {
    countDown(5);
    return 0;
}

A 5

B 4

C 6

D 1

💡 Hint

Remember the base case call also creates a stack frame.

The function calls itself with n=5 down to n=0. At n=0, the deepest call, there are 6 active stack frames (for n=5,4,3,2,1,0).