What is the output of the following C code?
int x = 5;
int y = ++x + x++;
printf("%d", y);
A11
B12
C13
DUndefined behavior
Correct Answer:
D. Undefined behavior
Explanation:
This code exhibits undefined behavior because x is modified twice between sequence points without an intervening sequence point. The result depends on the compiler's implementation.
What is the difference between scanf() and gets() functions?
Ascanf() can read formatted input while gets() reads only strings
Bgets() is safer than scanf()
CThere is no difference
Dscanf() stops at whitespace while gets() doesn't
Correct Answer:
A. scanf() can read formatted input while gets() reads only strings
Explanation:
scanf() reads formatted input based on format specifiers and stops at whitespace. gets() reads a string until a newline is encountered. Note: gets() is deprecated due to buffer overflow vulnerabilities.
What is the correct way to allocate memory for a single integer using malloc()?
Aint *ptr = (int *)malloc(sizeof(int));
Bint *ptr = malloc(sizeof(int));
Cint *ptr = (int *)malloc(4);
DBoth A and B
Correct Answer:
D. Both A and B
Explanation:
Both A and B are correct. Option A uses explicit type casting which is optional in C (not in C++). Option B avoids casting. Using sizeof(int) is preferred over hardcoding 4, as int size may vary across systems.
What happens when you use the strcpy() function without bounds checking?
AIt prevents buffer overflow automatically
BIt may cause buffer overflow if source string is longer than destination
CIt returns an error code
DIt truncates the source string automatically
Correct Answer:
B. It may cause buffer overflow if source string is longer than destination
Explanation:
strcpy() does not perform bounds checking. If the source string is longer than the destination buffer, it will write beyond the buffer boundary, causing a buffer overflow. This is a security vulnerability. Using strncpy() is safer.
What is the output of the following C code?
int arr[] = {10, 20, 30};
int *ptr = arr;
printf("%d", *(ptr + 1));
A10
B20
C30
DAddress of second element
Correct Answer:
B. 20
Explanation:
ptr points to arr[0]. ptr + 1 points to arr[1]. *(ptr + 1) dereferences to get the value at arr[1] which is 20. Pointer arithmetic adds sizeof(int) to the address for each increment.
Which of the following correctly describes the scope of a static variable declared inside a function?
ALocal to the function, retains value between function calls
BGlobal scope, initialized once
CLocal to the file only
DCreates a new instance on each function call
Correct Answer:
A. Local to the function, retains value between function calls
Explanation:
A static variable declared inside a function has local scope (visible only within that function) but persists for the entire program lifetime. Its value is retained between function calls and is initialized only once.
