Which control flow structure allows execution of code only if a certain condition is met?

The correct answer is B: if statement. The if statement executes a block of code conditionally. Loops repeat code, and switch cases are for multi-way branching based on a single expression.

Which memory segment stores global variables in C?

The correct answer is C: Data segment. Global variables are stored in the data segment (also called BSS segment for uninitialized globals). Local variables use the stack.

What does strlen() function return for the string "C2025"?

The correct answer is A: 5. strlen() counts characters before the null terminator. "C2025" has 5 characters, so strlen returns 5. The null terminator is not counted.

What is the purpose of the main() function in C?

The correct answer is C: Entry point of program execution. The main() function is the entry point where program execution begins. Every C program must have a main() function.

How much memory (in bytes) will the following structure occupy on a 32-bit system? struct Data { char c; int i; short s; };

The correct answer is C: 12. Due to padding/alignment: char(1) + padding(3) + int(4) + short(2) = 12 bytes on 32-bit systems.

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C Programming

C language from basics to advanced placement prep

490 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 71–80 of 490

Topics in C Programming

All Basics & Syntax 86 Data Types & Variables 97 Control Flow 100 Functions 99 Arrays & Strings 100 Pointers 99 Structures & Unions 100 File Handling 100 Dynamic Memory 98 Preprocessor 99

Q.71 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.

Test

Q.72 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.

Test

Q.73 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.

Test

Q.74 Medium Dynamic Memory

What is the correct way to allocate a dynamic array of struct for 'n' elements?
struct Node { int data; char name[20]; };

A struct Node *arr = malloc(n);

B struct Node *arr = malloc(n * sizeof(struct Node));

C struct Node arr = malloc(n);

D struct Node *arr = calloc(n, 1);

Correct Answer: B. struct Node *arr = malloc(n * sizeof(struct Node));

EXPLANATION

Must allocate n * sizeof(struct Node) bytes to hold all n structures.

Test

Q.75 Medium Dynamic Memory

In competitive exams, why is dynamic allocation preferred over static arrays for unknown input sizes?

A It's faster than static arrays

B Allows allocation only as much memory as needed, preventing stack overflow

C Static arrays don't work in C

D It's automatically freed by compiler

Correct Answer: B. Allows allocation only as much memory as needed, preventing stack overflow

EXPLANATION

Dynamic allocation allocates memory on heap based on runtime input, preventing fixed-size limitations and stack overflow.

Test

Q.76 Medium Dynamic Memory

If realloc() cannot expand memory at the current location, what does it do?

A Fails and returns NULL

B Allocates new memory, copies old data, frees old memory, returns new pointer

C Extends memory anyway

D Keeps old pointer valid

Correct Answer: B. Allocates new memory, copies old data, frees old memory, returns new pointer

EXPLANATION

realloc() finds new space if needed, copies data, deallocates old block, and returns new pointer.

Test

Q.77 Medium Dynamic Memory

What is the output of this code?
int *p = (int*)calloc(3, sizeof(int));
printf("%d %d %d", p[0], p[1], p[2]);

A Garbage values

B 0 0 0

C 3 bytes each

D Compiler error

Correct Answer: B. 0 0 0

EXPLANATION

calloc() initializes all allocated memory to zero, so all elements will be 0.

Test

Q.78 Medium Dynamic Memory

Which scenario best demonstrates a memory leak?

A char *s = malloc(10); free(s);

B char *s = malloc(10); s = malloc(20);

C char *s = malloc(10); free(s); free(s);

D char *s = NULL; free(s);

Correct Answer: B. char *s = malloc(10); s = malloc(20);

EXPLANATION

Original malloc(10) pointer is lost before freeing. The 10 bytes are now inaccessible - a memory leak.

Test

Q.79 Medium Dynamic Memory

What happens if you use a pointer after calling free() on it (without reallocating)?

A Program runs normally

B Pointer becomes NULL

C Use-after-free: undefined behavior, possible crash or data corruption

D Compiler automatically prevents it

Correct Answer: C. Use-after-free: undefined behavior, possible crash or data corruption

EXPLANATION

After free(), accessing the pointer causes undefined behavior as memory is returned to the heap and may be reused.

Test

Q.80 Medium Dynamic Memory

In dynamic 2D array creation:
int **arr = (int**)malloc(m * sizeof(int*));
what does the first malloc() allocate?

A m rows of integers

B An array of m pointers to int

C m*n integers

D Memory for entire 2D array at once

Correct Answer: B. An array of m pointers to int

EXPLANATION

First malloc allocates an array of m pointers. Each pointer must be individually allocated in a loop for actual row data.

Test

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