Govt. Exams
Entrance Exams
char *str = "Hello";
str[0] = 'J';
String literals are stored in read-only memory. Attempting to modify causes undefined behavior or segmentation fault.
int (*ptr)(int, int) declares a pointer to a function. int *ptr(int, int) declares a function returning pointer to int.
Valid pointer arithmetic includes addition/subtraction with integers and subtraction between pointers. Multiplication, division, and pointer addition are invalid.
void func(int *arr) { arr[0] = 100; }
int main() {
int a[5] = {1,2,3,4,5};
func(a);
printf("%d", a[0]);
}
Arrays are passed by reference (as pointers). Changes made in func() affect the original array. a[0] becomes 100.
char *str = "Hello";
printf("%c", *(str+1));
str points to 'H', str+1 points to 'e'. Dereferencing gives 'e'.
Calling free() on already freed memory or using a pointer after freeing it causes double-free errors and use-after-free bugs, leading to undefined behavior.
int x = 100, y = 200;
int *p = &x;
int *q = &y;
p = q;
printf("%d", *p);
p is reassigned to point to y (p = q). Dereferencing p now gives the value of y, which is 200.
int **p declares a pointer to a pointer (double pointer). Each * adds one level of indirection.
int *p, *q;
int x = 5;
p = &x;
q = p;
printf("%d %d", *p, *q);
Both p and q point to the same variable x. Dereferencing both gives the value 5.
calloc() takes two parameters (number of elements, size) and initializes all bytes to zero, while malloc() leaves memory uninitialized.
