# Data Structures - Stacks

16:   Stack can't be used to
 A. Evaluate an arithmetic expression in postfix form B. Implement recursion C. Convert a given arithmetic expression in infix form to its evaluate postfix form D. Allocate resources(like CPU)by the operating system Option: D Explanation :
17:   Which of the following permutations can be obtained in the output(in the same order),using a stack assuming that the input is the sequence 1,2,3,4,5 in that order?
 A. 3,4,5,1,2 B. 3,4,5,2,1 C. 1,5,2,3,4 D. 5,4,3,2,1 Option: B Explanation :
18:   Stack is useful for implementing
 A. Radix B. Breadth first search C. Recursion D. None of these Option: C Explanation :
19:

If the sequence of operations- push (1), push (2), pop, push (1), push (2), pop, pop, pop, push (2), pop, are performed on a stack, the sequenceof popped out values are

 A. 2, 2, 1, 1, 2 B. 2, 2, 1, 2, 2 C. 2, 1, 2, 2, 1 D. 2, 1, 2, 2, 2 Option: A Explanation :
20:

In evaluating the arithmetic expression 2 * 3-(4+5), using stacks to evaluate its equivalent post-fix form, which of the following stack configuration is not possible?

 A. B. C. D. Option: D Explanation : The postfix equivalent is 2 3 * 4 5 + -. For evaluating this using stack, starting from the left, we have to scan one by one. If it is an operand push. if it is an operator, pop it twice, apply the operator on the popped out entries and push the result onto the stack. If we follow this, we can find configuration in option (d) is not possible.