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C Programming

C language from basics to advanced placement prep

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Difficulty: All Easy Medium Hard 141–150 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.141 Medium Dynamic Memory

What happens if you call free() twice on the same pointer?

A Program immediately crashes

B Double free error - undefined behavior

C Memory is freed twice successfully

D No effect, second free is ignored

Correct Answer: B. Double free error - undefined behavior

EXPLANATION

Double free is undefined behavior and can cause program crash or corruption. After first free(), the pointer should not be used.

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Q.142 Medium Dynamic Memory

Consider a program that repeatedly allocates memory in a loop but never frees it. What problem occurs?

A Stack overflow

B Memory leak - heap memory is exhausted

C Segmentation fault immediately

D Integer overflow

Correct Answer: B. Memory leak - heap memory is exhausted

EXPLANATION

Allocating without freeing causes memory leak, where allocated memory is not returned to the system, eventually exhausting heap.

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Q.143 Medium Dynamic Memory

A competitive programmer allocates a 2D array dynamically. What is the correct approach?

A int **arr = (int**)malloc(rows * sizeof(int*)); for(i=0; i

B int arr[rows][cols] = (int**)malloc(...);

C int **arr = calloc(rows*cols, sizeof(int));

D int arr[][] = malloc(rows * cols);

Correct Answer: A. int **arr = (int**)malloc(rows * sizeof(int*)); for(i=0; i

EXPLANATION

2D arrays are allocated as array of pointers, where each row pointer points to a dynamically allocated array.

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Q.144 Easy Dynamic Memory

Which of the following correctly allocates memory for an array of 5 integers and initializes to zero?

A int *p = malloc(5 * sizeof(int));

B int *p = calloc(5, sizeof(int));

C int *p = realloc(NULL, 5);

D int p[5] = {0};

Correct Answer: B. int *p = calloc(5, sizeof(int));

EXPLANATION

calloc(5, sizeof(int)) allocates memory for 5 integers and initializes all to zero.

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Q.145 Easy Dynamic Memory

What is the primary difference between malloc() and calloc()?

A malloc() is faster than calloc()

B calloc() initializes memory with zeros, malloc() does not

C malloc() allocates from stack, calloc() from heap

D calloc() requires only one argument

Correct Answer: B. calloc() initializes memory with zeros, malloc() does not

EXPLANATION

calloc() allocates memory and initializes all bytes to zero, while malloc() leaves the allocated memory uninitialized.

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Q.146 Easy Dynamic Memory

What does free() function do in C?

A Allocates memory from heap

B Deallocates previously allocated memory

C Copies memory from one location to another

D Initializes memory with zeros

Correct Answer: B. Deallocates previously allocated memory

EXPLANATION

free() is used to deallocate memory that was previously allocated using malloc(), calloc(), or realloc().

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Q.147 Easy Dynamic Memory

Which header file must be included to use dynamic memory allocation functions in C?

A #include

B #include

C #include

D #include

Correct Answer: A. #include

EXPLANATION

stdlib.h contains declarations for malloc(), calloc(), realloc(), and free() functions.

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Q.148 Hard Dynamic Memory

What is the typical behavior if malloc() is called in a loop without corresponding free() calls?

A Program automatically clears memory

B Memory leaks accumulate, eventually causing program crash

C Compiler optimizes and prevents leaks

D Memory is recycled automatically

Correct Answer: B. Memory leaks accumulate, eventually causing program crash

EXPLANATION

Without freeing, allocated memory accumulates until system runs out of heap space, causing allocation failure or crash.

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Q.149 Hard Dynamic Memory

For a program handling 10^6 integers dynamically, which allocation is most appropriate?

A int arr[1000000];

B int *arr = malloc(1000000 * sizeof(int));

C static int arr[1000000];

D auto int arr[1000000];

Correct Answer: B. int *arr = malloc(1000000 * sizeof(int));

EXPLANATION

Stack allocation (option A) will cause stack overflow. Dynamic allocation on heap is required for large data.

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Q.150 Hard Dynamic Memory

What distinguishes a dangling pointer?

A A pointer that points to deallocated memory

B A pointer initialized to NULL

C A pointer that hasn't been malloc'd

D A pointer that points to stack variable

Correct Answer: A. A pointer that points to deallocated memory

EXPLANATION

Dangling pointer points to memory that has been freed. Accessing it causes undefined behavior.

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