11) List out any 3 differences between malloc and calloc functions in dynamic memory allocation?12) List out any six of the preprocessor directives available in the C programming language?13) Write a C program to pass structure as an argument to the functions using call by value method?14) Write a C program to demonstrate nested structure?15) List out any 3 differences between structure and Unions?

11. Differences between malloc and calloc functions in dynamic memory allocation:

a) malloc() allocates a single block of memory, whereas calloc() allocates multiple blocks of memory each of the same size and sets all bytes to zero.

b) The number of arguments differs. malloc() takes one argument: the number of bytes to allocate. calloc() takes two arguments: the number of elements to allocate and the size of each element.

c) malloc() does not initialize the memory allocated, while calloc() initializes the allocated memory to ZERO.

12. Six preprocessor directives available in the C programming language:

a) #include: This directive tells the C preprocessor to include the contents of the file specified in the input stream to the compiler.

b) #define: This directive is used to define a constant or macro.

c) #undef: This directive is used to undefine a constant or macro.

d) #ifdef: This directive checks if a macro is defined.

e) #ifndef: This directive checks if a macro is not defined.

f) #if: This directive checks if a condition is true.

13. C program to pass structure as an argument to the functions using call by value method:

#include<stdio.h>

struct student {
   char name[20];
   int roll_no;
};

void display(struct student stu);

int main() {
   struct student s;
   strcpy(s.name, "John");
   s.roll_no = 123;
   display(s);
   return 0;
}

void display(struct student stu) {
   printf("Name: %s\n", stu.name);
   printf("Roll No: %d\n", stu.roll_no);
}

14. C program to demonstrate nested structure:

#include<stdio.h>

struct date {
   int day;
   int month;
   int year;
};

struct student {
   char name[20];
   struct date dob;
};

int main() {
   struct student s;
   strcpy(s.name, "John");
   s.dob.day = 15;
   s.dob.month = 8;
   s.dob.year = 2000;
   printf("Name: %s\n", s.name);
   printf("Date of Birth: %d/%d/%d\n", s.dob.day, s.dob.month, s.dob.year);
   return 0;
}

15. Differences between structure and Unions:

a) In a structure, all members get memory allocated. In a union, memory is allocated for the largest member only.

b) In a structure, all members can be initialized at once, but in a union, only the first member can be initialized.

c) In a structure, all members can hold their value simultaneously, but in a union, only one member can hold a value at a time.