Question 1

What is the difference between stack and heap memory in C?

Accepted Answer

Stack is automatically managed for local variables; heap is manually managed with malloc/free. Stack memory is allocated/freed automatically when functions are called/return. Heap memory is allocated with malloc() and must be explicitly freed with free() — forgetting causes memory leaks.

Question 2

What is a memory leak in C?

Accepted Answer

Memory allocated with malloc() that is never freed, causing gradual memory exhaustion. A memory leak occurs when heap memory is allocated but never freed. Over time, the program's memory usage grows until the OS kills it or the system runs out of memory.

Question 3

What is the difference between pass by value and pass by reference in C?

Accepted Answer

Pass by value sends a copy of the data; pass by reference (via pointers) sends the address, allowing modification of the original. C passes arguments by value by default — the function receives a copy. To modify the original, pass a pointer (address). This is C's way of simulating pass by reference.

Question 4

What does the 'static' keyword do when applied to a local variable in a C function?

Accepted Answer

The variable retains its value between function calls instead of being re-initialized each time. A static local variable is initialized only once and persists for the program's lifetime. Unlike regular locals, it retains its value across multiple function calls.

Question 5

What is the key difference between malloc() and calloc() in C?

Accepted Answer

calloc() initializes the allocated memory to zero; malloc() leaves it uninitialized. malloc(n) allocates n bytes of uninitialized memory. calloc(count, size) allocates count*size bytes and initializes all bytes to zero. Use calloc when you need zero-initialized memory.

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