C++ -Problems in Stacking an array - c++

Question

I've been trying to figure out why my code isn't working correctly for the past few hours. Everything looks perfectly fine to me unless it's something I don't know about. I have asked my professor, but he can't seem to figure it out either. This code will completely ignore the if else statement in the push member function and will keep pushing after reaching the limit (in this case it's 5 elements). When it goes over the 5th element, and I check for the top, it shows the first implementation (element 0). I tried changing around my code by switching the member functions outside the class via scope resolution, but it's still no use. A different set of eyes would be greatly appreciated.
#include <iostream>
#include <cctype>
using namespace std;
class Stack
{
private:
static const int size = 5;
double myarr[size];
int t;
public:
Stack() { t = -1; }
void push(double element);
void pop();
void top();
void menu();
};
void Stack::push(double element)
{
if (t < size) {
t++;
myarr[t] = element;
}
else
cout << "Stack Limit Reach !!!" << endl;
}
void Stack::pop()
{
if (t >= 0) {
cout << "Element : " << myarr[t] << " was popped off the Stack " << endl;
t--;
}
else
cout << "No more elemnts in the Stack !!!" << endl;
}
void Stack::top()
{
if (t >= 0) {
cout << "Element : " << myarr[t] << " is at the top of the Stack " << endl;
}
else
cout << "No more elemnts in the Stack !!!" << endl;
}
void Stack::menu()
{
char choice = 'y';
int pick;
double elem;
while (toupper(choice) == 'Y');//while(choice == 'y' || choice == 'Y');
{
cout << "1. Push" << endl;
cout << "2. Pop" << endl;
cout << "3. Top" << endl;
cout << "4. Exit" << endl;
cin >> pick;
switch (pick)
{
case 1:
cout << "Enter the element: ";
cin >> elem;
cout << endl;
push(elem);
break;
case 2:
pop();
break;
case 3:
top();
break;
case 4:
choice = 'N';
break;
default:
cout << "Please select 1-4" << endl;
}
system("pause");
}
}
int main()
{
Stack obj;
obj.menu();
};

Answer 1

In your example code, the stack's size is 5 (which means array myarr has valid indices 0 through 4).
void Stack::push(double element)
{
if (t < size) {
t++;
myarr[t] = element;
}
else
cout << "Stack Limit Reach !!!" << endl;
}
Consider the case when t here is 4. The if tests true, so the block to add to myarr is entered. First thing that happens is you increment t, which is now 5. Then you use that as the index to store the value into myarr, which is out of bounds.
Try something like:
void Stack::push(double element)
{
if (t < size) {
myarr[t++] = element;
}
else
cout << "Stack Limit Reach !!!" << endl;
}

Answer 2

You are allowing 6 elements to be pushed onto the stack, and there's only room for 5.
Change:
if (t < size) {
t++;
to:
if (t < size-1) {
t++;

Answer 3

I understood your problem when you are searching for the top element you are not getting because whenever the stack becomes full for ex:-
assume you are inserting(below mentioned code) 5th element in 4th index it will be inserted and the value of t get incremented to 5 due to t++.
void Stack::push(double element)
{
if (t < size) {
t++;
myarr[t] = element;
}
else
cout << "Stack Limit Reach !!!" << endl;
}
but at the same time when you call top() function it checks for the index, and obviously 5 is greater that 0 so it enters the loop but index 5 contains '\0'
Character so there is an ambiguity with compiler
void Stack::top()
{
if (t >= 0) {
cout << "Element : " << myarr[t] << " is at the top of the Stack " << endl;
}
else
cout << "No more elemnts in the Stack !!!" << endl;
}
So the change that is required for the above code is just put a if statement by saying the compiler that if the stack is full then decrement t value by 1
void Stack::top()
{
if (t >= 0) {
if(t==size){t--;}
cout << "Element : " << myarr[t] << " is at the top of the Stack " << endl;
}
else
cout << "No more elemnts in the Stack !!!" << endl;
}
This may give you correct result

Answer 4

You skip myarr[0] then 5th element is saved to myarr[5] that is 6th element in myarr! (Accessing to elements of an array by index is zero based in C++)
Change:
Stack() { t = -1; }
to:
Stack() { t = 0; }
and
if (t < size) {
t++;
myarr[t] = element;
to:
if (t < size) {
myarr[t++] = element;