StackUsingArray

#include <iostream>
using namespace std;

class stack
{
 private:
 int top;
 int *arr;
 int n;

 public:
 stack(int x)
 {
 n=x;
 top=-1;
 arr=new int[n];
 for (int i=0;i<n;i++)
 arr[i]=0;
 }

 bool isempty()
 {
 if (top==-1)
 return true;
 else
 return false;
 }

 bool isfull()
 {
 if (top==(n-1))
 return true;
 else
 return false;
 }

 void push(int val)
 {
 if (isfull())
 cout<<"Stack Overflow"<<endl;
 else
 {
 top++;
 arr[top]=val;
 cout<<"Item pushed"<<endl;
 }
 }

 int pop()
 {
 if (isempty())
 cout<<"Stack underflow"<<endl;
 else
 {
 int t=arr[top];
 arr[top]=0;
 top--;
 return t;
 }
 return -1;
 }

 int count()
 {
 return (top+1);
 }

 int peek(int pos)
 {
 if (isempty())
 cout<<"Stack Underflow"<<endl;
 else if(pos>top)
 cout<<"Invalid position input"<<endl;
 else
 return arr[pos];
 return -1;
 }

 void change(int pos,int val)
 {
 if (pos>top)
 cout<<"Invalid position input"<<endl;
 else
 {
 arr[pos]=val;
 cout<<"Value changed at location "<<pos<<endl;
 }
 }

 void display()
 {
 if (isempty())
 cout<<"There are no elements in the stack"<<endl;
 else
 {
 cout<<"All the elements in the stack are as follows- "<<endl;
 for (int i=top;i>=0;i--)
 {
 cout<<arr[i]<<endl;
 }
 }
 }
};

int main()
{
 cout<<"Please enter the size of the stack"<<endl;
 int n=0;
 cin>>n;
 stack s(n);
 int option=0,pos=0,val=0;
 do
 {
 cout<<endl;
 cout<<"Please choose from the following options-"<<endl;
 cout<<"1. To perform the push opeation"<<endl;
 cout<<"2. to perform the pop operation"<<endl;
 cout<<"3. To check if the stack is empty"<<endl;
 cout<<"4. To check if the stack is full"<<endl;
 cout<<"5. To peek a value at a specific position"<<endl;
 cout<<"6. To count the total number of elements in the stack"<<endl;
 cout<<"7. To change an element at a specific position"<<endl;
 cout<<"8. To display all the elements in the stack"<<endl;
 cout<<"9. To clear the screen"<<endl;
 cout<<"10. To exit"<<endl;
 cout<<endl;

 cin>>option;
 switch(option)
 {
 case (1):
 {
 cout<<"Please enter the element that is to be pushed"<<endl;
 cin>>val;
 s.push(val);
 break;
 }
 case (2):
 {
 int x=s.pop();
 if (x!=-1)
 cout<<"The popped item is "<<x<<endl;
 break;
 }
 case (3):
 {
 if(s.isempty())
 cout<<"The stack is empty"<<endl;
 else
 cout<<"The stack is not empty"<<endl;
 break;
 }
 case (4):
 {
 if(s.isfull())
 cout<<"The stack is full"<<endl;
 else
 cout<<"The stack is not full"<<endl;
 break;
 }
 case (5):
 {
 cout<<"Enter the stack position to be peeked"<<endl;
 cin>>pos;
 if (s.peek(pos)!=-1)
 cout<<"The element at position "<<pos<<" is "<<s.peek(pos)<<endl;
 break;
 }
 case (6):
 {
 cout<<"The total number of elements in the stack are- "<<s.count()<<endl;
 break;
 }
 case (7):
 {
 cout<<"Please enter the position of the item to be changed"<<endl;
 cin>>pos;
 cout<<"Please enter the new value"<<endl;
 cin>>val;
 s.change(pos,val);
 break;
 }
 case (8):
 {
 s.display();
 break;
 }
 case (9):
 {
 system("cls");
 break;
 }
 default:
 {
 if (option!=10)
 cout<<"Please enter a valid option number"<<endl;
 }
 }
 }while (option!=10);
 cout<<"Program Terminated"<<endl;
 return 0;
}