Use cases - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pointer arithmetic in array traversal

What is the output of this C program that uses pointer arithmetic to traverse an array?

C

#include <stdio.h>

int main() {
    int arr[] = {10, 20, 30, 40};
    int *p = arr;
    printf("%d\n", *(p + 2));
    return 0;
}

A 10

B 20

C 30

D 40

💡 Hint

Remember that pointer arithmetic moves by the size of the data type.

The pointer p points to the first element of arr. Adding 2 moves it to the third element, which is 30.

🧠 Conceptual

intermediate

Use case of static variables inside functions

What is the main use case of a static variable declared inside a function in C?

A To keep the variable value persistent between function calls

B To make the variable accessible globally

C To allocate memory dynamically

D To declare a constant variable

💡 Hint

Think about what happens to a normal local variable after the function ends.

Static variables inside functions keep their value between calls, unlike normal local variables which are reinitialized each time.

🔧 Debug

advanced

Identify the error in this memory allocation use case

What error will this C code produce when run?

C

#include <stdio.h>
#include <stdlib.h>

int main() {
    int *ptr = malloc(5 * sizeof(int));
    ptr[5] = 10;
    printf("%d\n", ptr[5]);
    free(ptr);
    return 0;
}

A Memory leak error

B Segmentation fault due to out-of-bounds access

C Compilation error due to missing header

D No error, prints 10

💡 Hint

Check the valid index range for the allocated memory.

The array allocated has indices 0 to 4. Accessing ptr[5] is out of bounds and causes a runtime error.

📝 Syntax

advanced

Which option correctly declares a function pointer?

Which of the following is the correct syntax to declare a pointer to a function that takes an int and returns void?

A void (*funcPtr)(int);

B void *funcPtr(int);

C int (*funcPtr)(void);

D void funcPtr(*int);

💡 Hint

Function pointers use parentheses around *name.

Option A correctly declares funcPtr as a pointer to a function taking int and returning void.

🚀 Application

expert

Determine the output of this recursive use case

What is the output of this C program that uses recursion to calculate factorial?

C

#include <stdio.h>

int factorial(int n) {
    if (n <= 1) return 1;
    else return n * factorial(n - 1);
}

int main() {
    printf("%d\n", factorial(4));
    return 0;
}

A 1

B 10

C 120

D 24

💡 Hint

Factorial of 4 is 4*3*2*1.

The factorial function multiplies numbers from 4 down to 1, resulting in 24.