BInary addition oop

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

stack <int>read(int bits){
    stack <int>s;
    for(int i = 0; i < bits; i++){
        int n1;
        cout << "Enter digit " << i+1 << ": " << endl;
        cin >> n1;
        s.push(n1);
    }
    return s;
}

stack <int> add(stack <int>a1, stack <int>a2, int num){
    stack <int>add;
    int carry = 0;
    int n1 = 0, n2= 0, sum = 0;
    for(int i = 0; i < num; i++){
        n1 = a1.top();
        n2 = a2.top();
        a1.pop();
        a2.pop();
        sum = (n1 + n2 + carry)%2;
        add.push(sum);
        carry = (n1 + n2 + carry)/2;
    }
    if(carry == 1){
        add.push(carry);
    }
    return add;
}

void display(stack <int> dis){
    while(!dis.empty()){
        int t = dis.top();
        cout << t << " ";
        dis.pop();
    }
}

int main(){
    stack <int>s1, s2, s3;
    int n = 0;
    cout << "Enter no of bits" << endl;
    cin >> n;
    cout << "Enter stack 1 numbers: " << endl;
    s1 = read(n);
    cout << "Enter stack 2 numbers: " << endl;
    s2 = read(n);
    s3 = add(s1, s2, n);
    display(s3);
    return 0;
}