The first element of the stack

Question

How can i change the first element of a stack? Please, give me some advices

Answer 1

Hello Hakan Nihat

In which language?
And what are you trying to do. Can you give an example?

Answer 2

Unfortunately I am not familiar with c++.
But I think you have to use another stack to store the elements above the first element.

your stack:
4
3
2
1

2
3
1 4
stack a stack b

Now you can change the first element in stack a. After that you can put the other elements from stack b back to stack a.

Answer 3

``` #include <iostream>
using namespace std;

struct elem
{int key; elem *next;} *start=NULL,*temp=NULL;

elem *push(elem **st, int n);
elem *pop (elem **st, int &n);
void init (elem **st);
int empty (elem **st);

void main ()
{int nov;
init (&start);
int num;
cout<<"Input a value:\n";
while (cin>>num)
start=push(&start, num);
while (start->next==NULL)
{ temp=pop(&start,num);
cout<<num<<" ";}
cout<<endl;

cout<<"stoinost za possledniq element: ";
cin>>nov;
start->key=nov;
while(!(temp->next==NULL))
start=pop(&temp,num);

}

void init (elem **st)
{st=NULL;}

int empty(elem **st)
{
if (st==NULL)
return 1;
else
return 0;
}

elem *push (elem **st, int n)
{
elem *p;
p=new elem;
p->key=n;
p->next=*st;
*st=p;
return p;
}

elem *pop( elem **st, int &n)
{
elem *p;
n=(*st)->key;
p=*st;
*st=(*st)->next;
delete p;
return *st;}
```

Answer 4

C++. I have to reach to the last element and change it without losing previous ones

Answer 5

Yes, but how can i change it. That's my problem.

Answer 6

If you use pop() it returns the value, right?
To catch this value you should use a variable.

In pseudo code

int a = stackA.pop();

while(!stackA.isEmpty())

stackB.push(a);
a = stackA.pop();

end loop

now you can change a:
a = yourNumber;
put this back to stackA:
stackA.push(a);

refill stackA:

while(!stackB.isEmpty())

a = stackB.pop();
stackA.push(a);

end loop

But I am not sure if this is the best way. ;)