1. What is C language and why is it still used?

Answer:
C is a general-purpose, procedural programming language developed in 1972 by Dennis Ritchie.
It is still widely used because of its efficiency, portability, and close interaction with hardware. Many modern languages like C++, Java, and Python are based on C concepts.

2. What are the key features of C?

  • Simple and fast

  • Portable across platforms

  • Structured programming (functions)

  • Low-level access (pointers, memory management)

  • Large standard library

3. Difference between ++i and i++

  • ++i → Pre-increment → Increases i first, then returns value.

  • i++ → Post-increment → Returns current value, then increases i.

				
					#include <stdio.h>
int main() {
    int i = 5;
    printf("%d\n", ++i); // Output: 6
    printf("%d\n", i++); // Output: 6 (then i becomes 7)
    return 0;
}

4. What is a pointer in C?

Answer:
A pointer is a variable that stores the memory address of another variable.
They are widely used for dynamic memory allocation, arrays, and function arguments.

Example:

				
					#include <stdio.h>
int main() {
    int num = 10;
    int *ptr = &num;
    printf("Value: %d\n", *ptr);   // 10
    printf("Address: %p\n", ptr); // Memory address of num
    return 0;
}

5. What is the difference between malloc() and calloc()?

  • malloc() → Allocates a single block of memory (uninitialized).

  • calloc() → Allocates multiple blocks and initializes them to zero.

				
					int *a = (int*)malloc(5 * sizeof(int));   // Garbage values
int *b = (int*)calloc(5, sizeof(int));    // All values set to 0

6. What are storage classes in C?

They define the scope, lifetime, and visibility of variables.

  • auto → Default, local variable

  • register → Stored in CPU register (fast access)

  • static → Preserves value across function calls

  • extern → Declared globally, used across files

7. Common C Programming Tricky Question

Q: What will this code output?

				
					#include <stdio.h>
int main() {
    int a = 10;
    printf("%d %d %d", a, a++, ++a);
    return 0;
}

Answer:
The output is undefined behavior because the order of evaluation of function arguments is not specified in C.

8. Tips to Prepare for C Interviews

  • Revise C fundamentals: variables, loops, functions, arrays, pointers.

  • Practice DSA concepts in C (linked list, stack, queue, trees).

  • Solve common coding problems (palindrome, prime number, sorting).

  • Understand memory management (malloc, free, pointers).

  • Be clear about time complexity of common algorithms.