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));
memcpy() is the most efficient as it performs block memory copy. strcpy() is only for strings, and array assignment doesn't work in C.
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
For dynamic allocation, use double pointer char** and allocate memory for each string separately. Options B and C are static allocations.
What will the following code print?
A
10 20
B
10 30
C
20 20
D
Undefined behavior
Correct Answer:
D. Undefined behavior
This code exhibits undefined behavior due to lack of sequence points between modifications and access of p. Different compilers may produce different results.
What happens with this code?
A
Compilation error
B
String becomes 'PrXgramming'
C
Undefined behavior
D
No change to str
Correct Answer:
B. String becomes 'PrXgramming'
ptr points to the character array str. Modifying ptr[2] modifies str[2], changing 'o' to 'X', resulting in 'PrXgramming'.
Consider a 3D array: int arr[2][3][4]. How many elements total?
A
9 elements
B
24 elements
C
12 elements
D
6 elements
Correct Answer:
B. 24 elements
Total elements = 2 × 3 × 4 = 24 elements in the 3D array.
What is the output?
A
Hello
B
Helo
C
Garbage output
D
Compilation error
Correct Answer:
C. Garbage output
The array has 5 characters but is not null-terminated. printf("%s") will read beyond the array, printing garbage.
Which statement about 2D arrays in C is correct?
A
int arr[3][4] requires 12 contiguous bytes
B
arr[0] returns the address of the first row
C
arr[0][0] and *(*arr) access the same element
D
Both B and C
Correct Answer:
D. Both B and C
arr[0] points to the first row (array of 4 ints). arr[0][0] and *(*arr) both access the first element through pointer dereferencing.
What is the difference between arr[5] and *arr when arr is an array?
A
No difference, both access the same element
B
arr[5] accesses 6th element, *arr accesses 1st element
C
arr[5] is address, *arr is value
D
No valid comparison
Correct Answer:
B. arr[5] accesses 6th element, *arr accesses 1st element
arr[5] accesses the element at index 5 (6th element), while *arr (equivalent to arr[0]) accesses the first element.
How many times will the following loop execute?
A
4 times
B
5 times
C
Infinite loop
D
0 times
Correct Answer:
B. 5 times
Loop runs from i=0 to i=4, executing 5 times total. All array elements are initialized to 0.
What will be printed?
A
H
B
e
C
l
D
Compilation error
str+2 points to the 3rd character (index 2). *(str+2) dereferences it, printing 'l'.
