pop() is not working properly - c++

Question

Here is a c++ code on stack.Ignore the extra code here
#include<iostream>
using namespace std;
class mystack
{
private:
int top;
int size;
int * s;
public:
void initialize()
{
top=-1;
cin>>size;
s=new int[size];
}
~mystack(){delete [] s;}
void push()
{
int x;
if(top==size-1)
cout<<"stack overflow!"<<endl;
else
{
cout<<"Enter element to be pushed:";
cin>>x;
top++;
s[top]=x;
cout<<s[top]<<endl;
}
}
int pop()
{
int p=s[top];
if(top==-1)
return 0;
else
{
top--;
return p;
}
}
int maxsize()
{
return size;
}
int isempty()
{
if(top==-1)
return 0;
else
return 1;
}
void display()
{
int i,p=top;
cout<<s[0]<<endl;
for(i=0;i<=p;i++)
cout<<s[i]<<endl;
}
};
int main()
{
int n,i;
cout<<"Enter no. of stacks:";
cin>>n;
mystack * st=new mystack[n];
for(i=0;i<n;i++)
{
cout<<"Enter size of stack "<<i+1<<":";
st[i].initialize();
}
int c,s;
while(1)
{
cout<<"*****Operations*****"<<endl;
cout<<"1.Push 2.Pop 3.Maxsize 4.isempty 5.Display 6.Quit"<<endl;
cout<<"Enter your choice:";
cin>>c;
if(n>1)
{
cout<<"Operation on which stack:";
cin>>s;
}
else
s=1;
if(c==1)
st[s-1].push();
else if(c==2)
{
if(st[s-1].pop()==0)
cout<<"stack underflow!"<<endl;
else
cout<<st[s-1].pop()<<endl;
}
else if(c==3)
cout<<st[s-1].maxsize()<<endl;
else if(c==4)
{
if(st[s-1].isempty()==0)
cout<<"True"<<endl;
else
cout<<"False"<<endl;
}
else if(c==5)
st[s-1].display();
else if(c==6)
break;
else
{
cout<<"Wrong input!"<<endl;
continue;
}
}
return 0;
}
Here accessing pop operation gives the element of top-1.I can't understand why.What should I do?When I do return s[top--] same thing is happening.

Answer 1

Since you haven't gotten back to this, I am going to presume you've already found your logic error.
So here is the one error I found. There may be more, I quit looking ...
In the following code, how many times is pop() being called?
else if(c==2)
{
if(st[s-1].pop()==0)
cout<<"stack underflow!"<<endl;
else
cout<<st[s-1].pop()<<endl;
}