The Dreaded C Test

Continuing our focus on the C Test, here is a more generic 30-question test that’s challenging and fit for a 1-hour duration and requires a blend of conceptual, syntax, debugging, and problem-solving questions. The questions below are segmented into types and difficulty levels to cover a broad range of essential C programming topics. Most of these questions are intended to be short-answer or multiple-choice questions that test theoretical knowledge, code analysis, and quick coding skills, allowing candidates to work through them within the hour.

1. Basic Language Concepts (5 Questions)

What is the difference between malloc and calloc?
(Answer briefly or with a short code snippet.)
How does the const keyword affect a pointer in C?
(Describe the difference between const int *p, int * const p, and const int * const p.)
What is a segmentation fault, and why does it occur?
(Answer briefly.)
Explain the difference between stack and heap memory.
(Briefly describe use cases and differences in memory allocation.)
Why is sizeof(char) always 1 in C?
(Provide a brief explanation.)

2. Data Types and Pointers (5 Questions)

What is the output of the following code?

   int x = 10;
   int *p = &x;
   printf("%d\n", *p + x++);

Given the following declaration, how would you access the value at the second element of the third row?

   int matrix[4][5];

What will be the output of the following code?

   int a = 5, b = 10;
   int *ptr = &b;
   a = *ptr;
   *ptr = 20;
   printf("%d %d\n", a, b);

Write a C function that swaps two integers using pointers without using a temporary variable.
Explain the output of the following code:
c int a = 10; int *p1 = &a; int **p2 = &p1; printf("%d\n", **p2);

3. Strings and Arrays (5 Questions)

What is wrong with the following string initialization? char *str = "Hello, World!"; str[0] = 'h';
Write a function that reverses a string in place. (This is a quick coding question; keep it short.)
What will be the output of the following code? char str[] = "Hello"; printf("%c\n", str[6]);
How would you dynamically allocate a 2D array of integers in C? (Answer with a code snippet.)
Explain what’s wrong with this code and how to fix it:
c char str1[10] = "Hello"; char str2[10] = "World"; strcat(str1, str2);

4. Memory Management (5 Questions)

What happens if you free a pointer twice?
Explain what is wrong with this code: int *p = malloc(sizeof(int)); p = NULL; free(p);
Write a function that allocates memory for an integer array of n elements and initializes them to zero.
How would you check for a memory leak in a C program? (Briefly describe a method.)
What is the difference between realloc and malloc? (Brief answer.)

5. Structs and Unions (5 Questions)

Write a struct definition to represent a 3D point with x, y, and z coordinates.
What is a union, and how is it different from a struct?
Explain what’s wrong with the following code: struct Point { int x, y; } p; printf("%d\n", p.x);
How would you dynamically allocate memory for an array of 10 structs in C?
What will be the output of the following code?
c union Data { int i; float f; }; union Data d; d.i = 10; printf("%f\n", d.f);

6. Functions and Recursion (5 Questions)

What will be the output of the following recursive function call foo(3)? int foo(int n) { if (n == 0) return 1; return n * foo(n - 1); }
Explain why void main() is incorrect in C.
Write a function that calculates the nth Fibonacci number using recursion.
What is the purpose of the static keyword in the context of a function?
Describe what’s wrong with the following recursive function and how you’d fix it:
c void recurse() { recurse(); }

Summary

Total Questions: 30
Estimated Completion Time: 1 hour

This format mixes theoretical questions, debugging, and small coding tasks to comprehensively assess the candidate’s knowledge in C.

The Dreaded C Test – Part II