Go: package main

import (
        "fmt"
        "bufio"
        "os"
)

func main() {
        var n int
        var a, b string
        sc := bufio.NewScanner(os.Stdin)
        fmt.Scanf("%d", &n)
        for i := 0; i < n; i++ {
                sc.Scan()
                a = sc.Text()
                sc.Scan()
                b = sc.Text()

                if len(a) > len(b) {
                        s := add(a, b)
                        if s[len(a)] > 0 {
                                if len(a) >= 80 {
                                        fmt.Printf("overflow")
                                } else {
                                        for i := 0; i <= len(a);i++ {
                                                fmt.Printf("%d", s[len(a)-i])
                                        }
                                }
                                fmt.Printf("\n")
                        } else {
                                if len(a)-1 >= 80 {
                                        fmt.Printf("overflow")
                                } else {
                                        for i := 0; i < len(a);i++ {
                                                fmt.Printf("%d", s[len(a)-i-1])
                                        }
                                }
                                fmt.Printf("\n")
                        }
                } else {
                        s := add(b, a)
                        if s[len(b)] > 0 {
                                if len(b) >= 80 {
                                        fmt.Printf("overflow")
                                } else {
                                        for i := 0; i <= len(b);i++ {
                                                fmt.Printf("%d", s[len(b)-i])
                                        }
                                }
                                fmt.Printf("\n")
                        } else {
                                if len(b)-1 >= 80 {
                                        fmt.Printf("overflow")
                                } else {
                                        for i := 0; i < len(b);i++ {
                                                fmt.Printf("%d", s[len(b)-i-1])
                                        }
                                }
                                fmt.Printf("\n")
                        }
                }
        }
}

// expects ln > lm
func add(n string, m string) (s [100]int) {
        ln := len(n)
        lm := len(m)
        var sum [100]int

        for i := 0; i < ln; i++ {
                var s, t int
                s = int(n[ln-1-i]) - int('0')

                if lm - 1 - i >= 0 {
                        t = int(m[lm-1-i]) - int('0')
                } else {
                        t = 0
                }

                sum[i+1] = (s + t + sum[i]) / 10
                sum[i] = (s + t + sum[i]) % 10
        }

        return sum
}

C++: #include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<cmath>
#include<sstream>
#include<stack>
#include<map>
using namespace std;
#define pd pair<double,double>
	
	string rever(string a){
		string b=a;
		for(int i=0;i<a.size();i++)b[i]=a[a.size()-i-1];
		//cout<<b<<endl;
		return b;
	}
	
	int main(){
	string a,b,c;
	int n;
	cin>>n;
	for(int i=0;i<n;i++){
	cin>>a>>b;
	c="ssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss";
	if(a.size()<b.size())swap(a,b);
	b=rever(b);
	cout<<c<<endl;
	//cout<<a<<" "<<b<<endl;
	for(int i=0;i<=a.size()-b.size();i++){b.push_back('0');}
	b=rever(b);
	int as=a.size();
	bool kuriagari=false;
	for(int i=as-1;i>=0;i--){
		int n1=a[i]-'0';
		int n2=b[i]-'0';
		int ans=0;
		ans=n1+n2;
		if(kuriagari)ans++;
		if(ans>=10){
		kuriagari=true;
		ans-=10;
		}
		else kuriagari=false;
		c[i]=ans+'0';
	}
	
	if(c.find("s")!=string::npos){
		int fin=c.find("s");
		c.erase(fin);
	}
	//cout<<c<<endl;
	
	if(c.size()<80)cout<<c<<endl;
	else cout<<"overfllow"<<endl;
	}
    return 0;
}

C++: #include<iostream>
#include<cstring>
using namespace std;
#define MAX 90
#define temp 85
int main(){
	int x,A[MAX],B[MAX],al,bl,sum[MAX],pre,now;
	char a[MAX],b[MAX];
	cin>>x;
	while(x-->0){
		for(int i=0;i<MAX;i++){
			A[i]=0;
			B[i]=0;
			sum[i]=0;
		}
		cin>>a;
		cin>>b;
		al=strlen(a);
		bl=strlen(b);
		for(int i=0;i<al;i++)
		A[i]=a[al-1-i]-'0';
		for(int i=0;i<bl;i++)
		B[i]=b[bl-1-i]-'0';
		if(al>bl)
		bl=al;
		pre=0;
		for(int i=0;i<=bl;i++){
			if(A[i]+B[i]+pre>9)
				now=1;
			else now=0;
			sum[i]=(A[i]+B[i]+pre)%10;
			pre=now;
		}
		
		if(sum[bl]!=0){
		for(int i=bl;i>=0;i--)
		cout<<sum[i];
		}
		else {
		for(int i=bl-1;i>=0;i--)
		cout<<sum[i];
		}
		
		
		cout<<endl;
		
		
		
	}
	return 0;
}

C++: #include <iostream>
#include <string>
#include <stack>
#include <cstdlib>

using namespace std;

int main() {
  int N;
  
  cin >> N;

  for (int N_i = 0; N_i < N; N_i++) {
    string str_data1, str_data2;
    cin >> str_data1;
    cin >> str_data2;

    stack<int> data1, data2; 
    for (int data1_i = 0; data1_i < str_data1.size(); data1_i++) {
      char buff[2];
      buff[0] = str_data1[data1_i];
      buff[1] = '\0';
      data1.push(atoi(buff));
    }
    for (int data2_i = 0; data2_i < str_data2.size(); data2_i++) {
      char buff[2];
      buff[0] = str_data2[data2_i];
      buff[1] = '\0';
      data2.push(atoi(buff));
    }

    stack<int> sum;
    int carry = 0;
    int flag = data1.size() < data2.size() ? 0 : 1;
    while(flag == 0 ? !data1.empty() : !data2.empty()) {
      int presum = data1.top() + data2.top() + carry;
      carry = presum / 10;
      sum.push(presum % 10);
      data1.pop();
      data2.pop();
    }
    stack<int> *data;
    data = data1.size() > data2.size() ? &data1: &data2;
    while(!data->empty()) {
      int presum = data->top() + carry;
      carry = presum / 10;
      sum.push(presum % 10);
      data->pop();
    }

    if (carry != 0)
      sum.push(carry);

    for (int sum_i = 0; !sum.empty(); sum_i++) {
      cout << sum.top();
      sum.pop();
    }
    cout << endl;
  }

  return 0;
}

C++: #include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int main(){
	int n,m;
	string aindex, bindex, ans;
	cin >> m;
	n = 0;
	string a,b;
	for(int j = 0; j < m; j++){
		cin >> a >> b;
		if(a.size()>=79||b.size()>=79){
			cout << "overflow" << endl;
		}else{
			for(int i = 0; i< max(a.size(),b.size()); i++){
				if(a.size()>= i+1){
					aindex = a[a.size()-i-1];
				}else{
					aindex = "0";
				}
				if(b.size() >= i+1){
					bindex = b[b.size()-i-1];
				}else{
					bindex = "0";
				}
				n = stoi(aindex) + stoi(bindex) + (n-n%10==10);
				aindex = to_string(n%10);
				ans = aindex + ans;
			}
			if(ans.size()>=79){
				cout << "overflow" << endl;
			}else{
				if(n-n%10 == 10){
					ans = '1' + ans;
				}
				cout << ans << endl;
			}
		}
		ans ="";
		n = 0;
	}
	return 0;
}