Code

#include<bits/stdc++.h>
using namespace std;
string findSum(string str1, string str2)
{
 if (str1.length() > str2.length())
  swap(str1, str2);
 string str = "";
 int n1 = str1.length(), n2 = str2.length();
 reverse(str1.begin(), str1.end());
 reverse(str2.begin(), str2.end());
 int carry = 0;
 for (int i=0; i<n1; i++)
 {
  int sum = ((str1[i]-'0')+(str2[i]-'0')+carry);
  str.push_back(sum%10 + '0');
  carry = sum/10;
 }
 for (int i=n1; i<n2; i++)
 {
  int sum = ((str2[i]-'0')+carry);
  str.push_back(sum%10 + '0');
  carry = sum/10;
 }
 if (carry)
  str.push_back(carry+'0');
 reverse(str.begin(), str.end());
 return str;
}
int main()
{
 string n1;
 string n2;
 cin >> n1;
 cin >> n2;
 cout << findSum(n1, n2);
 return 0;
}

#include <bits/stdc++.h>
#define ll long long

using namespace std;
string add(string a, string b){
    string c = "";
    int l, n1 = a.size(), n2 = b.size(), carry = 0, sum;
    if (n1 > n2) l = n1; else l = n2;
    while (a.size() < l) a = '0' + a;
    while (b.size() < l) b = '0' + b;
    for (int i=l-1; i>=0; i--){
        sum = (int)(a[i]-48)+(int)(b[i]-48)+carry;
        carry = sum/10;
        c = char(sum%10+48)+c;
    }
    if (carry > 0) c = '1' + c;
    return c;
}
int main(){
    string a, b; cin >> a >> b;
    cout << add(a,b) << '\n';
    return 0;
}