CBSE Guess > Papers > Important Questions > Class XII > 2010 > Computer Science > Computer Science By Ravi Kiran
CBSE CLASS XII
DELHI . 2002
Q.1. Given the following class,
char *msg[ ]={“over flow”,”under flow”};
class Stack
{ int top; //the stack pointer
int stk[5]; //the elements
void err_rep(int e_num)
{ cout<<msg[e_enum]; //report error message
}
public:
void init( )
{ top=0;
} //initialize the stack pointer
void push(int); //put new value in stk
void pop( ); //get the top value.
};
Define pop outside the Stack. In your definition take care of under flow condition. Function pop
should invoke err_rep to report under flow.
Solution:
void Stack::pop( )
{
}
Q.2. Change the following infix expression into postfix expression. (A+B)*C+D/E-F .
Ans:
Children, Try this answer as an assignment.
DELHI : 2001
Q.1.Write an algorithm to convert an infix expression to postfix expression.
Ans:
The following algorithm transforms the infix expression X into its equivalent postfix expression Y.
The algorithm uses a stack to temporarily hold operators and left parentheses. The postfix expression
Y will be constructed from left to right using the operands from X and the operators which are
removed from STACK. We begin by pushing a left parenthesis onto STACK and adding a right
parenthesis at the end of X. The algorithm is completed when STACK is empty.
Algorithm:
Suppose X is an arithmetic expression written in infix notation. This algorithm finds the equivalent
postfix expression Y.
1. Push “(“ onto STACK, and add “)” to the end of X.
2. Scan X from left to right and REPEAT Steps 3 to 6 for each element of X UNTIL the STACK is
empty.
3. If an operand is encountered, add it to Y.
4. If a left parenthesis is encountered, push it onto STACK.
5. If an operator is encountered, then:
(a) Repeatedly pop from STACK and add to Y each operator(on the top of STACK) which has the
same precedence as or higher precedence than operator.
(b) Add operator to STACK.
/* End of If structure */
6. If a right parenthesis is encountered, then:
(a) Repeatedly pop from STACK and add to Y each operator (on the top of STACK) until a left
Parenthesis is encountered.
(b) Remove the left parenthesis. (Do not add the left parenthesis to Y).
/* End of If structure */
Paper By Mr. Ravi Kiran
Email Id : [email protected]
