# NCERT Solutions for Class 12 Computer Science (C++) – Stack

NCERT Solutions for Class 12 Computer Science (C++) – Stack

### Short Answer Type Questions-I[2 marks each]

Question 1.
Evaluate the following postfix expression. Show the status of stack after execution of each operation separately:
2,13, + , 5, -,6,3,/,5,*,<

 ITEM SCANNED OPERATION STACK 2 PUSH 2 2 13 PUSH 13 2,13 + POP 13 and 2 Evaluate 2 + 13 = 15 PUSH 15 15 5 PUSH 5 15,5 – POP 5 & 15 EVALUATE 15-5 = 10 PUSH 10 10 6 PUSH 6 10, 6 3 PUSH 3 10, 6, 3 / POP 3 & 6 EVALUATE 6/3= 2 PUSH 2 10,2 5 PUSH 5 10, 2, 5 * POP 5 & 2 EVALUATE 2*5 = 10 PUSH 10 10, 10 < POP 10 & 10 EVALUATE 10<10 = FALSE PUSH FALSE FALSE

RESULT = FALSE

Question 2.
Evaluate the following postfix expression : (show status of Stack after each operation)
100,40,8,/,20,10,-,+,*

 ITEMSCANNED OPERATION STACK 100 PUSH 100 100 40 PUSH 40 100,40 8 PUSH 8 100,40,8 / POP 8 POP 40 EVALUATE 40/8 =5 PUSH 5 100,5 20 PUSH 20 100,5,20 10 PUSH 10 100, 5, 20, 10 POP 10 POP 20 EVALUATE 20-10 =10 PUSH 10 100,5,10 + POP 10 POP 5 EVALUATE 10 + 5= 15 PUSH 15 100,15 * POP 15 POP 100 EVALUATE 100 * 15 = 1500 PUSH 1500 1500

Question 3.
Evaluate the following postfix expression. Show the status of stack after execution of each operation separately:
T, F, NOT, AND, T, OR, F, AND

 S.No. Scanned Element Operation Stack 1 True PUSH True True 2 False PUSH False False 3 NOTCalculate NOT False POP FalsePUSH True TrueTrue, True 4 Andcalculate:True AND True POP True POP TruePUSH True TrueTrue 5 True PUSH True True, True 6 ORCalculate: True OR True POP TruePUSH True TrueTrue 7 False PUSH False True, False 8 ANDCalculate: True AND False POP FalsePOP True PUSH False TrueFalse

Thus the stack will have False Value

Question 4.
Evaluate the following postfix expression. Show the status of stack after execution of each operation separately:
F, T, NOT, AND, F, OR, T, AND

 S.No. Scanned Element Operation Stack 1 F PUSH F F 2 T PUSH T F,T 3 NOTCalculate NOT T POP TPUSH F FF,F 4 ANDCalculate NOT POP FPOP FPUSH F FF 5 F PUSH F F,F 6 OR POP FPOP F 7 T PUSH T F,T 8 AND POP TPOP FPUSH F FF

Thus the stack will have False Value

Question 5.
Evaluate the following postfix expression using a stack and show the contents of stack after execution of each operation:
5,3,2, *, 4,2, /, -,*

 SYMBOL STACK OUTPUT 5 5 3 5,3 2 5,3,2 * PUSH 3,2Perform 3*2=6POP 6 555,6 4 5,6,4 2 5,6,4,2 / PUSH 4,2Perform 4/2=2POP2 5,65,65,6,2 – PUSH 6,2Perform 6-2=4POP 4 555,4 * PUSH 5,4perform 5*4=20.POP 20 20

Result=20

Question 6.
Evaluate the following POSTFIX notation. Show status of Stack after every step of evaluation (i.e. after each operation)
False NOT, True, AND, True, False, OR, AND

 Element Scanned Stack Status False False NOT True True True, True AND True True True, True False True, True, False OR True, True AND True

Question 7.
Top is a pointer variable pointing to the top element of a stack, with each node having the following structure declaration:
struct Stack {int Data, Stack * Next};
Considering the above explanation, what will the following code do ?
int count = 0, Sum = 0;

```Stack * Temp = Top;
while (Temp - > Next! = NULL)
{ count + +;
Sum + = Temp - > Data;
Temp Temp - > Next;
}
count < < Sum / count;```

It will calculate the average of stack values.

Question 8.
Convert the expression ((x * 3 + y * 3 + z * 3) / (x + y + z)) into postfix expression. Show the content of the stack during the conversion.
Given expression : ((x * 3 + y * 3 + z * 3) / (x + y + z))
((x * 3 + y * 3 + z * 3) / (x + y + z))

 SymbolScanned Stack Expression ((X* (((((((* ——XX 3+yX-3+zX-3)/(X+y+Z)) ((*((* +((* +((* + *((* + *((* + * +((* + * +((* + * + *((* + * + *((/(/((/((/(+(/(+

\Postfix expression is: x3y3z3 * + * + * xyz + +/

Question 9.
Evaluate the following POSTFIX expression, show the status of Stack after execution of each operation separaterly:
45,45,+,32,20,10,/,-,*

 Element Scanned Stack Status 45 45 45 45,45 + 90 32 90,32 20 90,32,20 10 90,32,20,10 / 90,32,2 – 90,30 * 2700

Hence the final result is 2700

Question 10.
Convert the following Infix expression to its equivalent Postfix expression, showing the stack contents for each step of conversion.
P/Q+(R-T)*U
P/Q+(R-T)*U = (P/Q+(R-T)*U)

 Element Stack of Operator PostfixExpression ( ( P ( P / (/ P Q

### Short Answer Type Questions-II[3 marks each]

Question 1.
Write the definition of a member function Pop ()
in C++, to delete a book from a dynamic stack of TEXTBOOKS considering the following code is already included in the program.

```Struct TEXTBOOKS
{
Char ISBN [20]; Char TITLE [80]; TEXTBOOKS *Link;
};
class STACK
{
TEXTBOOKS *Top;

public :
STACK () {Top = NULL;}

void Push ();
. void pop );
-STACK ();
};```

```void STACK : : POP ()
{
if (Top ! = NULL)
{
TEXTBOOKS *Temp;
Temp=Top;
cout<< TOP- >ISBN<<Top-
TITLE<<"delected"<<endl;
delete Temp;
}
else
cout<<"Stack Empty"<<endl;
}```

OR
Any other correct equivalent function definition

Question 2.
Write the defintion of a member function PUSH () in C+ +, to add a new book in a dynamic stack of BOOKS considering the following code is already included in the program :

```struct BOOKS
{
Char ISBN [20]; TITLE[80];
};
class STACK
{
BOOKS *Top;
public :
STACK () {Top = NULL;}
void PUSH ();
Void POP ();
-STACK ();
};```

```void STACK :: PUSH ()
{
BOOKS *Temp;
Temp=New BOOKS;
gets (Temp->ISBN);
gets (Temp->TITLE);
Top=Temp;
}```

OR
Any other correct equivalent function definition

Question 3.
Convert the expression (A-5)*6+(10/B)/2 to corresponding postfix expression. Also show the status of operator stack after each step.
((A-5)*6+(10/B)/2)

 ScannedElements Stack Status Output ((A–5)*6+(10/B)/2) (((((((-((-((*(*(+(+((+((+(/(+(/(+(+/(+/ AAA, 5A, 5,-A, 5,-A, 5, -, 6A, 5, -, 6*A, 5,-, 6,*A, 5,     6, *, 10A, 5, -, 6, *, 10A, 5,     6, *, 10, BA, 5,-, 6,10, B/A, 5,    6,10, B JA, 5,-, 6, *, 10, B/,2A,5,-,6,M0,By,2y,+

The correspondence postfix expression is A, 5, 6, 10, B, /,2, /,+

### Long Answer Type Questions[4 marks each]

Question 1.
Convert the following Infix expression to its equivalent Postfix expression, showing the stack contents for each step of conversion.
A/(B+C)*D-E
A/ (B + C) *D-E

 Element Stack Expression A/(B+C)★D–E ((/(/C(/c(/c+(/c+(*(*(-(- AAAABABABCABC+ABC+/ABC+/DABC+/D*ABC+/D*E-

Question 2.
Write definition for a function DISPMID (int A[][5], int R, int C) in C+ + to display the elements of middle row
and middle column from a two dimensional array A having R number of rows and C number of columns.
For example, if the content of array is as follows:

 215 912 516 401 515 103 901 921 802 601 285 209 609 360 172

The function should display the following as output:
103 901 921 802
601 516 921 609

```void DISPMID (int A[] [5] , int R, int C)
{
int mid = (R+C)/2;
for (int i=0; i<c; i++)
{
Cout << A[mid] [i]<<"";
} cout<<endl;
for (int i=0; i<R; i++)
cout << A[i][mid]<<"";
}```

Question 3.
Convert the following Infix expression to its equivalent Postfix expression, showing the stack contents for each step of conversion.
P/(Q-R)*S+T
P/(Q-R)*S+T
BODMAS : PQR-/S*T+
PQR-/S*T+

 Element Stack Expression P/(Q–R)*S+T) ((/(/c(/c(/c-(/c-(/(*(*(+(+ PPPPQPQPQRPQR-PQR-/PQR-/SPQR-/S*PQR-/S*TPQR-/S*T+

Question 4.
Convert the following infix expression to its equivalent postfix expression, showing the stack contents for each step of conversion:
X/Y+U*(V-W)
X / Y + U* (V – W) = ((X / Y) + (U * (V – W)))

 Element Stack Postfix ( ( X X / / X Y / XY ) XY/ + + XY/ ( + XY/ U + XY/U * + * XY/U ( + * XY/U V + * XY/UV – + *- XY/UV W + *- XY/UVW ) + * XY/UVW- ) + XY/UVW-* ) it XY/UVW-* +

OR

 Element Stack Postfix X X / / X Y / XY + + XY/ U + XY/U * + * XY/U ( + *( XY/U V + *( XY/UV – + *(- XY/UV w + ‘(- XY/UVW ) + * XY/UVW- XY/UW-* XY/UVW-* +

OR

Any other method or converting the given Infix expression to its equivalent Postfix expression showing stack contents

Question 5.
Evaluate the following postfix expression using stack and show the contents after excecution of each.
Operations : 470,5,4,∧,25,/,6,*

 S. No. Symbol Operation Stack Result 1 470 push(470) 470 2 5 push(5) 470,5 3 4 push(4) 470,5,4 4 /N P°P(4) 470,5 0 pop(5) 470 perform(5∧4) push(625) 470,625 5 25 push(25) 470,625,25 6 / pop(25) 470,625 pop(625) 470 perform(625/25) 470 push(25) 470,25 7 6 push(6) 470,25,6 8 * pop(6) 470,25 pop(25) 470 perform(25*6) 470

Question 6.
Write member functions to perform POP and PUSH operations in a dynamically allocated stack containing the objects of the following structure:

```struct Game
{ char Gamename[30];
int numofplayer;
Game *next; } ;```

```struct Game
{
char Gamename[3 0] ;
int numofplayer;
Game *next;
};
class Stack { Game *Top;
public :
Stack ()
{
Top = NULL;
}
void Push();
void Pop();
void display();
-Stack();
} ;
void Stack::Push()
{
Game *temp = new Game;
cout<<"Enter Data : "; gets(temp->Gamename);
cin>>temp->numofplayer;
temp->next =Top;
Top = temp;
}
void Stack:: Pop()
{
if ( Top != NULL)
{
Game *temp = Top;
cout<Gamename<<" Deleted"; Top = Top->next;
delete temp;
}
else
cout<<"Stack is empty....";
}```

Question 7.
Write a function PUSHBOOK() in C++ to perform insert operation on Dynamic Stack, which contains Book_no and Book_Title. Consider the following definition of NODE, while writing your C+ + code,

```struct NODE
{
int Book_No ;
char Book_Title [20];
NODE * Next;
};```

```Void PUSHBOOK (NODE *TOP> int Book_No, char B Title [20])
{
NODE*temp;
temp=new NODE;
temp —> Book_No=Book_No;
Strcpy (temp —> Book_Title, B Title) ;
temp --> Next=NULL ;
if (Top==NULL)
Top=temp;
else
{
temp —> Next=top;
Top==temp;
}
}```

Question 8.
Write a function POPBOOK( ) in C++ to perform delete operation from a Dynamic Stack, which contains Bno and Title. Consider the following definition of NODE, while writing your C++code.

```struct NODE
{
int Bno;
char Title[20] ;
} ;```

```node*PopBOOK(node*TOP int Bno, char B Title [20])
{
node*temp;
temp=new node;
temp —>Bno=Bno;
strcpy (temp —>Title, B Title);
if (TOP==NULL)
Top=Temp;
else
{
TOP==temp;
}
}```

Question 9.
Write the definition of a member function push() for a class Library in C++ to insert a book information in a dynamically allocated strack of books considering the following code is already written as a part of the program

```struct book
{
int bookid;
char bookname[20];
book*next;
} ;
class Library
{
book*top;
public
Library()
{
top=NULL;
}
void push();
void pop();
void disp() ;
-Library();
};```

```void Library: :push()
{
book*nptr;
nptr=new book;
cout<<"Enter values for bookid and bookname"; cin> >nptr->bookid;
gets(nptr->bookname);
nptr->next =NULL;
if (top==NULL)
top=nptr;
else
{
nptr->next=top,
top=nptr;
}
}```

Question 10.
Convert the following Infix expression to its equivalent Postfix expression, showing the stack contents for each step of conversion:
U * V + R / (S-T)
U*V + R/(S-T)

 Element Stack Postfix ( ( U U * * V UV ) UV* + + ( R UV*R / +/ ( S UV*RS – +/- T UV*RST ) UV*RST- ) UV*RST-/ ) UV*RST-/+

OR

 U U * * U V * UV + + UV* R + UV*R / +/ UV*R ( +/( UV*R S +/( UV*RS – +/(- UV*RS T +/(- UV*RST ) +/ UV’RST- + UV’RST-/ UV*RST-/+

OR

Any other method for converting the given Infix expression to its equivalent Postfix expression showing stack contents.

+