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<vector>
#include<iostream>
#include<iomanip>
#include<string>
#include<cstdlib>

typedef std::vector<int> bignum;

const int e9=1000000000;

bignum add(const bignum& a,const bignum& b);
bignum subtract(const bignum& a,const bignum& b);
void output(const bignum& num);
int compare(const bignum& a,const bignum& b);
bignum newnum(const std::string& str);

int main()
{
	bignum a,b,sum;
	std::string str;
	int n;
	std::cin>>n;
	for(int i=0;i<n;i++)
	{
		std::cin>>str;
		a=newnum(str);
		std::cin>>str;
		b=newnum(str);
		sum.clear();
		sum=add(a,b);
		if(compare(sum,newnum("10000000000000000000000000000000000000000000000000000000000000000000000000000000"))>=0)
		{
			std::cout<<"overflow"<<std::endl;
		}
		else
		{
			output(sum);
		}
	}
}

bignum add(const bignum& a,const bignum& b)
{
	bignum sum;
	int carry=0;
	long long temp;
	for(int i=0;i<((a.size()>b.size())?a.size():b.size())||carry==1;i++)
	{
		temp=carry;
		carry=0;
		if(i<a.size())
		{
			temp+=a[i];
		}
		if(i<b.size())
		{
			temp+=b[i];
		}
		sum.push_back(temp%e9);
		if(temp>=e9)
		{
			carry=1;
		}
	}

	return sum;
}

int compare(const bignum& a,const bignum& b)
{
	if(a.size()>b.size()){return 1;}
	else if(a.size()<b.size()){return -1;}
	else
	{
		for(int i=a.size()-1;i>=0;i--)
		{
			if(a[i]>b[i]){return 1;}
			else if(a[i]<b[i]){return -1;}
		}
	}
	return 0;
}

bignum newnum(const std::string& str)
{
	bignum num;
	int len;
	for(int i=str.size();i>=0;i-=9)
	{
		len=9;
		if(i<9)len=i;
		num.push_back(atoi(str.substr(i-len,len).c_str()));
	}
	return num;
}

void output(const bignum& num)
{
	for(int i=num.size()-1;i>=0;i--)
	{
		if(i==num.size()-1)
		{
			std::cout<<num[i];
		}
		else
		{
			std::cout<<std::setfill('0')<<std::setw(9)<<std::right<<num[i];
		}
	}
	std::cout<<std::endl;
}

C++: #include<cstdio>
#include<algorithm>
#include<string.h>
//#include<string>

using namespace std;

#define MAX(x,y) ((x>y)? x:y)


int n;//データセットの数

char str[2][10000];//	入力される整数文字列
int n_str[2];//長さを収納

char answer[85];

FILE *fp=stdin;

int main()
{
	fscanf(fp,"%d",&n);
	for(int i=0;i<n;i++)
	{
		sta:
		fscanf(fp,"%s%s",&str[0],&str[1]);
		for(int j=0;j<2;j++)n_str[j]=strlen(str[j]);
		int max =0,min=1;
		if(n_str[1]>n_str[0])
		{
			max=1;
			min=0;
		}
		int s = n_str[max]-n_str[min];
		char cha[85];
		fill(cha,cha+80,'0');
		for(int j=n_str[min];j>=0;j--)
		{
			cha[j+s]=str[min][j];
		}
		strcpy(str[min],cha);
		fill(answer,answer+85,0);
		for(int j=n_str[max]-1;j>=0;j--)
		{
			answer[j]=str[0][j]+str[1][j]-'0';
			if(answer[j]>'9')//繰り上がり時の処理
			{
				answer[j]-=10;
				if(j==0)
				{
					if(n_str[max]>=80)
					{
						n_str[max]++;
					}

					else printf("1");
				}
				else str[0][j-1]++;
			}
		}
		if(n_str[max]>80)
		{
			printf("overflow\n");
		}
		else printf("%s\n",answer);
	}
	fclose(fp);
	return 0;
}

C++: //#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
//#include "bits/stdc++.h"

#define rep(i,n) for(ll (i)=0;(i)<(ll)(n);(i)++)
#define all(x) (x).begin(),(x).end()

#define MOD 1000000007LL
#define INF (1LL<<60LL)
#define int long long
#define MAX_N (100001)
typedef long long ll;

using namespace std;

string stringsum(string s1, string s2) {
	if (s1 == s2 && s1 == "0") return "0";
	string s;
	reverse(all(s1));
	reverse(all(s2));
	int len1 = s1.size();
	int len2 = s2.size();
	bool up = false;
	for(int i=0;i<=100;i++) {
		//cout << i << endl;
		if (len1 <= i && len2 <= i)break;
		int k = 0;
		if (up) {
			k++;
			up = false;
		}
		string c;
		if (len1>i){
			c = s1[i];
			k += stoi(c);
		}
		if (len2 > i) {
			c = s2[i];
			k += stoi(c);
		}
		if (k >= 10) {
			up = true;
			k -= 10;
		}
		s += to_string(k);
		//cout << k << " ";
		//cout << s << endl;
	}
	if (up)s += '1';
	reverse(all(s));
	return s;
}


signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n; cin >> n;
	rep(i, n) {
		string s1, s2;
		cin >> s1 >> s2;
		string s;
		s = stringsum(s1, s2);
		if (s.size() > 80) cout << "overflow" << endl;
		else cout << s << endl;
	}
}