What is the output of this code? void swap(int a, int b) { int temp = a; a = b; b = temp; } int main() { int x = 5, y = 10; swap(x, y); printf("%d %d", x, y); }

The correct answer is B: 5 10. This is call-by-value. The function swaps copies of x and y, not the originals. Original values remain unchanged.

Which initialization method for structures is used in designated initializers (C99 feature)?

The correct answer is B: struct s obj = {.x = 1, .y = 2};. Designated initializers (C99) allow specifying members by name using dot notation, making code more readable and maintainable.

Which structure feature is most suitable for implementing a state machine with limited states?

The correct answer is A: Bit fields. Bit fields efficiently store boolean/limited-range states using minimal memory, ideal for state machines.

Which of the following is NOT a valid string initialization?

The correct answer is C: char str[10]; str = "Program";. Array names are constant pointers and cannot be reassigned. Direct assignment to char array after declaration is invalid.

What will be the output of the following code? int *ptr = malloc(sizeof(int)); if(ptr == NULL) printf("Failed"); else printf("Success");

The correct answer is B: Success. In typical scenarios, malloc() successfully allocates memory and returns non-NULL pointer, printing 'Success'. NULL check is good practice for error handling.

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C Programming

C language from basics to advanced placement prep

197 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 111–120 of 197

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.111 Hard Arrays & Strings

What is the relationship between pointer arithmetic and array indexing in C?

A Pointer arithmetic is faster than array indexing

B arr[i] is equivalent to *(arr + i) - both are mathematically identical

C Array indexing is only for static arrays, pointer arithmetic for dynamic

D No relationship - they are completely different operations

Correct Answer: B. arr[i] is equivalent to *(arr + i) - both are mathematically identical

EXPLANATION

C standard defines arr[i] as *(arr + i). Both notations access the same memory location and perform identically.

Test

Q.112 Hard Arrays & Strings

What is the most efficient way to copy one array to another in C?

A memcpy(dest, src, sizeof(src));

B strcpy(dest, src);

C for loop with element-by-element assignment

D Array assignment dest = src;

Correct Answer: A. memcpy(dest, src, sizeof(src));

EXPLANATION

memcpy() is the most efficient as it performs block memory copy. strcpy() is only for strings, and array assignment doesn't work in C.

Test

Q.113 Hard Arrays & Strings

How should dynamic 1D array of strings be declared for 5 strings of length 20?

A char **str = (char**)malloc(5 * sizeof(char*)); for loop to allocate each string

B char str[5][20];

C char *str[5];

D Both A and C after proper allocation

Correct Answer: A. char **str = (char**)malloc(5 * sizeof(char*)); for loop to allocate each string

EXPLANATION

For dynamic allocation, use double pointer char** and allocate memory for each string separately. Options B and C are static allocations.

Test

Q.114 Hard Arrays & Strings

What will the following code print?
int arr[3] = {10, 20, 30};
int *p = arr;
printf("%d %d", *p++, *++p);

A 10 20

B 10 30

C 20 20

D Undefined behavior

Correct Answer: D. Undefined behavior

EXPLANATION

This code exhibits undefined behavior due to lack of sequence points between modifications and access of p. Different compilers may produce different results.

Test

Q.115 Hard Arrays & Strings

What happens with this code?
char *ptr;
char str[] = "Programming";
ptr = str;
ptr[2] = 'X';

A Compilation error

B String becomes 'PrXgramming'

C Undefined behavior

D No change to str

Correct Answer: B. String becomes 'PrXgramming'

EXPLANATION

ptr points to the character array str. Modifying ptr[2] modifies str[2], changing 'o' to 'X', resulting in 'PrXgramming'.

Test

Q.116 Hard Arrays & Strings

What will happen?
char arr[5] = "Hello";
printf("%d", strlen(arr));

A 5

B 6

C Compilation error

D Undefined behavior

Correct Answer: C. Compilation error

EXPLANATION

Array is too small. "Hello" needs 6 bytes including null terminator, but only 5 are allocated. This causes buffer overflow.

Test

Q.117 Hard Arrays & Strings

In a dynamic 2D array created as: int **arr = (int**)malloc(rows * sizeof(int*)); What is the next step?

A Directly assign values to arr[i][j]

B Allocate memory for each row

C Call free() immediately

D Use strdup() to copy strings

Correct Answer: B. Allocate memory for each row

EXPLANATION

After allocating the array of pointers, each row must be allocated separately.

Test

Q.118 Hard Arrays & Strings

In the declaration int *arr[10], what is arr?

A Array of 10 pointers to int

B Pointer to array of 10 integers

C Array of 10 integers

D Pointer to 10 pointers

Correct Answer: A. Array of 10 pointers to int

EXPLANATION

int *arr[10] declares an array of 10 pointers to int (subscript binds tighter than dereference). Use int (*arr)[10] for pointer to array.

Test

Q.119 Hard Arrays & Strings

What is the correct way to safely copy strings in modern C?

A strcpy(dest, src)

B strncpy(dest, src, sizeof(dest)-1); dest[sizeof(dest)-1]='\0';

C sprintf(dest, "%s", src)

D memcpy(dest, src, strlen(src))

Correct Answer: B. strncpy(dest, src, sizeof(dest)-1); dest[sizeof(dest)-1]='\0';

EXPLANATION

strncpy with buffer size check and explicit null termination is the standard safe approach. Option A lacks bounds checking; C and D have issues with null termination.

Test

Q.120 Hard Arrays & Strings

If ptr is a pointer to int array and ptr = arr, what does ptr[3] represent?

A The 4th element of the array (same as arr[3])

B The address 3 positions ahead in memory

C 12 bytes ahead of array start (assuming 4-byte int)

D Both A and C are true

Correct Answer: D. Both A and C are true

EXPLANATION

ptr[3] is equivalent to arr[3] and accesses the element at address *(ptr+3). For int*, ptr+3 moves 12 bytes (3×4 bytes) in memory.

Test

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