BSc Sem 1 Computer Paper 2017 Answers of 3 B, C, D

Question 3 (B) answer in brief (Any one)                                                                           2 marks

1.      Structure vs. Class.

Comparison between Class and Structure in C++:

	Class	Structure
Definition	A class in C++ can be defined as a collection of related variables and functions encapsulated in a single structure.	A structure can be referred to as a user defined data type possessing its own operations.
Keyword for the declaration	Class	Struct
Default access specifier	Private	Public
Example	struct student { private:     int data; public:    void getdata();    void dispdata(); };	struct student {    int data;    void getdata();    void dispdata(); };
Purpose	Data abstraction and further inheritance	Generally, grouping of data
Type	Reference	Value
Usage	Generally used for large amounts of data.	Generally used for smaller amounts of data.

2.      Explain Union.

A union is a special data type available in C that allows to store different data types in the same memory location. You can define a union with many members, but only one member can contain a value at any given time. Unions provide an efficient way of using the same memory location for multiple-purpose.

Defining a Union

To define a union, you must use the union statement in the same way as you did while defining a structure. The union statement defines a new data type with more than one member for your program. The format of the union statement is as follows −

union [union tag] {

   member definition;

   member definition;

   ...

   member definition;

} [one or more union variables];  

The union tag is optional and each member definition is a normal variable definition, such as int i; or float f; or any other valid variable definition. At the end of the union's definition, before the final semicolon, you can specify one or more union variables but it is optional.

#include <stdio.h>

#include <string.h>

union Data {

   int i;

   float f;

   char str[20];

};

int main( ) {

   union Data data;       

   printf( "Memory size occupied by data : %d\n", sizeof(data));

   return 0;

}

Question 3 (C) answer in detail (Any one)                                                                          3 marks

1.       Explain malloc() function.

Allocating Memory Dynamically

While programming, if you are aware of the size of an array, then it is easy and you can define it as an array. For example, to store a name of any person, it can go up to a maximum of 100 characters, so you can define something as follows −

char name[100];

But now let us consider a situation where you have no idea about the length of the text you need to store, for example, you want to store a detailed description about a topic. Here we need to define a pointer to character without defining how much memory is required and later, based on requirement, we can allocate memory as shown in the below example −

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

int main() {

   char name[100];

   char *description;

   strcpy(name, "Piyush Patel");

   /* allocate memory dynamically */

   description = malloc( 200 * sizeof(char) );

   if( description == NULL ) {

      fprintf(stderr, "Error - unable to allocate required memory\n");

   }

   else {

      strcpy( description, "Piyush Patel a DPS student in class 10th");

   }

   printf("Name = %s\n", name );

   printf("Description: %s\n", description );

}

When the above code is compiled and executed, it produces the following result.

Name = Piyush Patel

Description: Piyush Patel a DPS student in class 10th

2.       Explain new and delete.

new and delete Operators

There is following generic syntax to use new operator to allocate memory dynamically for any data-type.

new data-type;

Here, data-type could be any built-in data type including an array or any user defined data types include class or structure. Let us start with built-in data types. For example we can define a pointer to type double and then request that the memory be allocated at execution time. We can do this using the new operator with the following statements −

double* pvalue  = NULL; // Pointer initialized with null

pvalue  = new double;   // Request memory for the variable

The memory may not have been allocated successfully, if the free store had been used up. So it is good practice to check if new operator is returning NULL pointer and take appropriate action as below −

double* pvalue  = NULL;

if( !(pvalue  = new double )) {

   cout << "Error: out of memory." <<endl;

   exit(1);

}

The malloc() function from C, still exists in C++, but it is recommended to avoid using malloc() function. The main advantage of new over malloc() is that new doesn't just allocate memory, it constructs objects which is prime purpose of C++.

At any point, when you feel a variable that has been dynamically allocated is not anymore required, you can free up the memory that it occupies in the free store with the ‘delete’ operator as follows −

delete pvalue;        // Release memory pointed to by pvalue

Let us put above concepts and form the following example to show how ‘new’ and ‘delete’ work −

#include <iostream>

using namespace std;

int main () {

   double* pvalue  = NULL; // Pointer initialized with null

   pvalue  = new double;   // Request memory for the variable

   *pvalue = 29494.99;     // Store value at allocated address

   cout << "Value of pvalue : " << *pvalue << endl;

   delete pvalue;         // free up the memory.

   return 0;

}

If we compile and run above code, this would produce the following result −

Value of pvalue : 29495

Question 3 (D) write a note on (Any one)                                                                            5 marks

1.       Explain Array of Structure.

There can be array of structures in C programming to store many information of different data types. The array of structures is also known as collection of structures.

Let's see an example of structure with array that stores information of 5 students and prints it.

#include<stdio.h>  

#include<conio.h>  

#include<string.h>  

struct student{  

int rollno;  

char name[10];  

};  

void main(){  

int i;  

struct student st[5];  

clrscr();  

printf("Enter Records of 5 students");  

  

for(i=0;i<5;i++){  

printf("\nEnter Rollno:");  

scanf("%d",&st[i].rollno);  

printf("\nEnter Name:");  

scanf("%s",&st[i].name);  

}  

  

printf("\nStudent Information List:");  

for(i=0;i<5;i++){  

printf("\nRollno:%d, Name:%s",st[i].rollno,st[i].name);  

}  

  

getch();  

}  

Output:

Enter Records of 5 students

Enter Rollno:1

Enter Name:Sonoo

Enter Rollno:2

Enter Name:Ratan

Enter Rollno:3

Enter Name:Vimal

Enter Rollno:4

Enter Name:James

Enter Rollno:5

Enter Name:Piyush

Student Information List:

Rollno:1, Name:Sonoo

Rollno:2, Name:Ratan

Rollno:3, Name:Vimal

Rollno:4, Name:James

Rollno:5, Name:Piyush

2.       Write a program using structure to display student roll no., name and age.

#include <stdio.h>  

#include <string.h>  

struct student    

{   int rno;    

    char name[50];    

    float age;    

}s1;  //declaring s1 variable for structure  

int main( )  

{  

   //store first student information  

   s1.rno=101;  

   strcpy(s1.name, "Piyush Patel");//copying string into char array  

   s1.age=32;  

  

   //printing first student information  

   printf( "student 1 rno : %d\n", s1.rno);  

   printf( "student 1 name : %s\n", s1.name);  

   printf( "student 1 age : %f\n", s1.age);  

  

   return 0;  

}

Output:

student 1 rno : 101

student 1 name : Piyush Patel

student 1 age : 32.000000