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C Programming

C language from basics to advanced placement prep

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Difficulty: All Easy Medium Hard 131–140 of 1,000

Topics in C Programming

All Basics & Syntax 100 Data Types & Variables 100 Control Flow 100 Functions 100 Arrays & Strings 100 Pointers 100 Structures & Unions 100 File Handling 100 Dynamic Memory 100 Preprocessor 100

Q.131 Easy Dynamic Memory

Which header file must be included to use malloc() and free() functions?

A #include

B #include

C #include

D #include

Correct Answer: A. #include

EXPLANATION

<stdlib.h> is the standard header file containing declarations for malloc(), calloc(), realloc(), and free() functions.

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Q.132 Easy Dynamic Memory

Which function in C is used to allocate memory dynamically at runtime?

A malloc()

B alloc()

C allocate()

D memalloc()

Correct Answer: A. malloc()

EXPLANATION

malloc() is the standard C library function for dynamic memory allocation. It takes the number of bytes to allocate as an argument and returns a pointer to the allocated memory.

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Q.133 Hard Dynamic Memory

For implementing a dynamic stack in competitive programming, which memory management approach is best?

A Pre-allocate fixed size array on stack

B Single malloc for max capacity, track top with index

C malloc/free for each push/pop operation

D Use global static array

Correct Answer: B. Single malloc for max capacity, track top with index

EXPLANATION

Single allocation with index tracking minimizes malloc/free overhead, suitable for competitive programming time constraints.

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Q.134 Hard Dynamic Memory

Consider this: char *p = malloc(10); strcpy(p, "Hello World"); What occurs?

A String is copied successfully

B Buffer overflow - writes beyond allocated 10 bytes

C Null terminator is lost

D Compilation error

Correct Answer: B. Buffer overflow - writes beyond allocated 10 bytes

EXPLANATION

"Hello World" is 11 bytes (including null terminator). Writing to 10-byte buffer causes buffer overflow, corrupting adjacent memory.

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Q.135 Hard Dynamic Memory

What is a potential issue when allocating very large contiguous blocks (>10^8 bytes) dynamically?

A malloc() always succeeds for any size

B Fragmentation and allocation failure, should check return value

C Integer overflow in size calculation

D Free space is automatically allocated

Correct Answer: B. Fragmentation and allocation failure, should check return value

EXPLANATION

Large allocations may fail due to heap fragmentation or insufficient contiguous memory. Always check malloc() return for NULL.

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Q.136 Medium Dynamic Memory

In 2024-2025 competitive exams, for storing variable number of test cases (up to 10^5), which approach is optimal?

A Fixed array of size 10^5

B Dynamic allocation with exact size needed

C Multiple calls to realloc() as data arrives

D Use stack allocation for speed

Correct Answer: B. Dynamic allocation with exact size needed

EXPLANATION

Reading input size first, then allocating exact size is optimal for memory efficiency and avoids repeated realloc() overhead.

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Q.137 Medium Dynamic Memory

What is the critical issue with this code? int *p = (int*)malloc(sizeof(int)); free(p); p = NULL;

A Cast to (int*) is unnecessary

B Setting p=NULL after free is good practice but not done immediately

C No issue, this is safe practice

D malloc size is too small

Correct Answer: C. No issue, this is safe practice

EXPLANATION

This shows safe practice: allocation, use, freeing, and immediately setting pointer to NULL to avoid use-after-free.

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Q.138 Medium Dynamic Memory

For a graph with V vertices and E edges stored dynamically, what is typical space complexity?

A O(1)

B O(V + E) for adjacency list, O(V²) for adjacency matrix

C O(E²)

D O(V*E)

Correct Answer: B. O(V + E) for adjacency list, O(V²) for adjacency matrix

EXPLANATION

Adjacency list uses dynamic allocation proportional to V+E, while matrix uses fixed V² space regardless of actual edges.

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Q.139 Medium Dynamic Memory

A program uses realloc() to expand an array from 100 to 200 elements. The old address is p. After realloc():?

A p still points to old memory location

B p is automatically updated to new location

C Must assign returned value: p = realloc(p, ...)

D The array content is lost

Correct Answer: C. Must assign returned value: p = realloc(p, ...)

EXPLANATION

realloc() returns a new pointer (old location may move). Must use: p = realloc(p, newsize) and check for NULL.

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Q.140 Medium Dynamic Memory

In a competitive programming scenario, you need to store strings dynamically. What is safe practice?

A char *str = malloc(100); without checking for NULL

B char *str = malloc(strlen(input)+1); with NULL check and strncpy

C char str[100] always on stack

D No allocation needed, use global arrays

Correct Answer: B. char *str = malloc(strlen(input)+1); with NULL check and strncpy

EXPLANATION

Safe practice includes allocating exact size (input length + 1 for null terminator), checking for NULL, and using bounded string functions.

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