int to char problem ?

#include<iostream>
#include<vector>
#include<string>
using namespace std;
class Stack
{
public :
    Stack();
    void push(char&);
    void pop();
    char getpop();
    void output();

private:
    vector<char> _vector;
    int topOfStack;
};
Stack::Stack():topOfStack(-1){}
void Stack::push(char &x)
{
    topOfStack++;
    _vector.push_back(x);
}
void Stack::pop()
{
    topOfStack--;
}
char Stack::getpop()
{
    return _vector[topOfStack--];
}
void Stack::output()
{
    for(int i = topOfStack-1; i != -1 ; i--)
    {
        cout<<"item "<<i<<"= "<<_vector[i]<<endl;
    }
}

int main()
{
    string _str;
    cin>>_str;
    Stack _stack;
    for(int i=0 ;i != _str.size(); i++)
    {
        if((_str[i] != '+') && (_str[i] != '*'))
        {
            _stack.push(_str[i]);
        }
        else if(_str[i] == '+')
        {
            int temp;
            temp = _stack.getpop() + _stack.getpop();
            char ctemp = (char)temp;
            _stack.push(ctemp);
        }
        else if(_str[i] == '*')
        {
            int temp;
            temp = _stack.getpop() * _stack.getpop();
            char ctemp = (char)temp;
            _stack.push(ctemp);
        }
    }
    cout<<endl;
    _stack.output();
    return 0;
}

I have problem in line

        else if(_str[i] == '+')
        {
            int temp;
            temp = _stack.getpop() + _stack.getpop();
            char ctemp = (char)temp;
            _stack.push(ctemp);
        }
        else if(_str[i] == '*')
        {
            int temp;
            temp = _stack.getpop() * _stack.getpop();
            char ctemp = (char)temp;
            _stack.push(ctemp);
        }

b'coz ex. 56+
5 => 53
6 => 54
sum is 107 => k but i want 11 not k and push in vector is 11 plese
help.