Question

What is the output of the following code? stackList stack; int x, y; x = 2; y = 3; stack.push(8); stack.push(x); stack.push(x + 5); y = stack.top(); stack.pop(); stack.push(x + y); x = stack.top(); stack.pop(); cout << "x = " << x << endl;

Answer 1

Stack is LIFO data structure (Last In First Out) where the last element entered in stack will be the last one to be out of stack. It has three operations: push() : used to insert an element in stack, pop() : used to delete an element from the stack, top() : used to return the top of the stack i.e. the newest member of the stack. All these operations will take place at the top.

Explanation:

Now, looking at the program, x and y are initialized the values of 2 and 3 respectively. The stack pushes 8 onto the stack making it the first member of the stack. Then the value of x which is 2 is pushed onto the stack. Next, (x+5) = (2+5) = 7 is pushed onto the stack.

Pop() is used to delete hence 7 is popped out from the stack. top() is assigned to y which is 2 in this case and again 2 is popped out from the stack. Now, (x+y) = (2+2) = 4 is pushed onto the stack. And the top() is assigned to x which is 4. 4 is again popped out from the stack. Hence the value of x is 4.