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 <cstdio>
#include <string>
using namespace std;

#define rep2(x,from,to) for(int x=(from);(x)<(to);(x)++)
#define rep(x,to) rep2(x,0,to)
int main() {
	int n;
	cin >> n;
	while(n--) {
		string a, b;
		int x[84], y[84], s[84], max;
		cin >> a >> b;
		if(a.length() > 80 || b.length() > 80) {
			cout << "overflow" << endl;
			continue;
		}
		int i = 0, j = 0;
		for(; a[i] != '\0'; ++i) {
			x[i] = a[i] - '0';
		}
		for(; b[j] != '\0'; ++j) {
			y[j] = b[j] - '0';
		}
		
		if(i > j) {
			for(int k = j - 1; k >= 0; k--) {
				y[i-j+k] = y[k];
			}
			rep(k,i-j) {
				y[k] = 0;
			}
			max = i;
		} else if(i < j) {
			for(int k = i - 1; k >= 0; k--) {
				x[j-i+k] = x[k];
			}
			rep(k,j-i) {
				x[k] = 0;
			}
			max = j;
		} else max = i;
		bool f = 0;
		for(int k = max - 1; k >= 0; k--) {
			int c = x[k] + y[k];
			if(f) c++;
			if(c >= 10) {
				f = 1, c -= 10;
			} else f = 0;
			s[k] = c;
		}
		if(f) {
			max++;
		}
		if(max > 80) cout << "overflow" << endl;
		else {
			string ans;
			if(f) {
				ans += "1";
				max--;
			}
			rep(k,max) {
				ans += s[k] + '0';
			}
			cout << ans << endl;
		}
	}
	return 0;
}

C++: #include<cstdio>
#include<algorithm>
#include<vector>
#include<string>
#include<iostream>
#include<queue>
#include<map>
#include<set>
#include<complex>
#include<stack>
 
using namespace std;
 
int main(){
     
    int n;
    cin>>n;
     
	while(n-- > 0){
        vector<int> ans;
        vector<int> a;
        vector<int> b;
         
        string c,d;
        cin>>c>>d;
         
		for(int i = 0; i < (int)c.size(); ++i){
            a.push_back(c[c.size()-1-i]-'0');
        }
		for(int i = 0; i < (int)d.size(); ++i){
            b.push_back(d[d.size()-1-i]-'0');
        }
         
         
        int kuri = 0;
        while(!a.empty() || !b.empty() || kuri!=0){
            int sum = kuri;
            kuri = 0;
             
            if(!a.empty()){
                sum += a[0];
                a.erase(a.begin());
            }
             
            if(!b.empty()){
                sum += b[0];
                b.erase(b.begin());
            }
             
            ans.push_back(sum%10);
            kuri += sum/10;
        }
         
        if(ans.size()>80)puts("overflow");
        else{
			for(int i = 0; i < (int)ans.size(); ++i){
                printf("%d",ans[ans.size()-1-i]);
            }puts("");
        }
    }
     
}

/*
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	
	int n;
	cin >> n;
	
	while(n-- > 0){
	
	string str1;
	cin >> str1;
	
	string str2;
	cin >> str2;
	
	reverse(str1.begin(), str1.end());
	reverse(str2.begin(), str2.end());
	
	int check;
	if(str1.size() > str2.size()){
		check = 1;
	}
	else if(str1.size() == str2.size()){
		check = 2;
	}
	else {
		check = 3;
	}
	
	int ans[100];
	bool next = false;
	int short_ = min(str1.size(), str2.size());
	int long_ = max(str1.size(), str2.size());	
	if(long_ >= 80){
		cout << "overflow" << endl;
		continue;
	}

	for(int i = 0; i < short_; ++i){
		int num = 0;
		num += (str1[i] - '0') + (str2[i] - '0');
		if(next){
			num++;
		}
		ans[i] = num;
		next = false;	
		if(num >= 10){
			num -= 10;
			ans[i] -= 10;
			next = true;
		}
	}
	
	if(check == 1){
		for(size_t i = str2.size(); i < str1.size(); ++i){
			int num = str1[i] - '0';
			if(next){
				num++;
			}
			ans[i] = num;
			next = false;	
			if(num >= 10){
				num -= 10;
				ans[i] -= 10;
				next = true;
			}
		}
		if(next){
			ans[str1.size()] = 1;
			long_ ++;
		}
	}	
	
	if(check == 3){
		for(size_t i = str1.size(); i < str2.size(); ++i){
			int num = str2[i] - '0';
			if(next){
				num++;
			}
			ans[i] = num;
			next = false;	
			if(num >= 10){
				num -= 10;
				ans[i] -= 10;
				next = true;
			}
		}
		if(next){
			ans[str2.size()] = 1;
			long_ ++;
		}
	}
	
	if(long_ >= 80){
		cout << "overflow" << endl;
		continue;
	}

	for(int i = long_ - 1; i >= 0; --i){
		cout << ans[i];
	}	
	cout << endl;
	}
		
	return 0;
}
*