Get minimum element from stack

/*
The structure of the class is as follows
class _stack{
stack<int> s;
int minEle;
public :
    int getMin();
    int pop();
    void push(int);
};
*/

/*returns min element from stack*/
int _stack :: getMin()
{
   //Your code here
   if(s.empty())
        return -1;
   return minEle;
}

/*returns poped element from stack*/
int _stack ::pop()
{
    if (s.empty()==true){ 
        return -1; 
    } 
    int t = s.top(); 
    int x;
    s.pop(); 

    if (t < minEle){
        x=minEle;
        minEle = 2*minEle - t; 
    } 
    else
        return t;
    return x;
}

/*push element x into the stack*/
void _stack::push(int x){
    if (s.empty()) { 
        minEle = x; 
        s.push(x); 
        return; 
    } 
    if (x < minEle) { 
        s.push(2*x - minEle); 
        minEle = x; 
    } else
       s.push(x); 
}