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 <bits/stdc++.h>
#define rep(i,l,n) for(int i=l;i<n;i++)
#define all(a) a.begin(),a.end()
using namespace std;

/*int main(){
	int n;
	cin>>n;
	rep(i,0,n){
		string s1,s2;
		cin>>s1>>s2;

		if(s1.size()<s2.size()) swap(s1,s2);

		for(int j=s1.size()-1,k=s2.size()-1;j>=0;j--,k--){
			if(k>=0) s1[j]+=s2[k]-'0';
			if(s1[j]>'9'){
				s1[j]-=10;
				if(s2)
			}
			ans[j]=a%10;
			ans[j+1]=a/10;
			//cout<<" "<<j<<" "<<ans[j]<<endl;
		}
		if(ans[80]>0){
			cout<<"overflow"<<endl; return 0;
		}
		bool f=0;
		for(int i=80;i>=0;i--){
			if(f==0 && ans[i]>0){
				f=1; cout<<ans[i];
			}else if(f) cout<<ans[i];
		}
		cout<<endl;
	}
}*/

int main(){
    int n;
    cin>>n;
    rep(i,0,n){
        int ans[85]={};
        vector<int> n1(80,0),n2(80,0);
        //rep(j,0,81)cout<<n1[j]<<" "<<n2[j]<<endl;
        string s1,s2; 
        cin>>s1>>s2;
        //cout<<s1<<" "<<s2<<endl;
        int sz1=s1.size(),sz2=s2.size();
 
        //rep(j,0,sz1) n1[j]=s1[sz1-1-j]-'0';
        //rep(j,0,sz2) n2[j]=s2[sz2-1-j]-'0';
 		
 		reverse(all(s1));
 		reverse(all(s2));

        rep(j,0,s1.size()) n1[j]=s1[j]-'0';
        rep(j,0,s2.size()) n2[j]=s2[j]-'0';

        reverse(all(n1));
        reverse(all(n2));

        for(int j=79;j>=0;j--){
           // cout<<"  "<<j<<" "<<n1[j]<<" "<<n2[j]<<endl;
            ans[j]+=n1[j]+n2[j];
            if(ans[j]>9){
            	if(j>0) {
            		ans[j-1]=1;
            		ans[j]-=10;
            	}
            }
            //cout<<" "<<j<<" "<<ans[j]<<endl;
        }
        if(ans[0]>9){
            cout<<"overflow"<<endl; break;
        }
        bool f=0;
        for(int j=0;j<80;j++){
            if(f==0 && ans[j]>0){
                f=1; cout<<ans[j];
            }else if(f) cout<<ans[j];
        }
        cout<<endl;
    }
}

C++: #include <iostream>
#include <string>
#include <cstdio>
#include <algorithm>
#include <stdexcept>

class biglong {
	static const int part_digits = 8;
	static const int max_parts = 10;
	static const int max_digits = part_digits * max_parts;
	static const unsigned long max_part_value = 100000000;
	unsigned long parts[max_parts];
public:
	biglong(unsigned long value) : parts() { parts[0] = value; }
	biglong(const biglong& rhs) {
		std::copy(rhs.parts, rhs.parts + max_parts, parts);
	}
	explicit biglong(const std::string& rhs) : parts() {
		if (rhs.size() > max_digits) {
			throw std::overflow_error("biglong overflow");
		}
		int part_count = (static_cast<int>(rhs.size()) + part_digits - 1) / part_digits;
		int pos = static_cast<int>(rhs.size());
		for (int i = 0; i < part_count; ++i) {
			pos -= part_digits;
			if (pos < 0) {
				parts[i] = std::atol(rhs.substr(0, pos + part_digits).c_str());
			} else {
				parts[i] = std::atol(rhs.substr(pos, part_digits).c_str());
			}
		}
	}
	biglong& operator+=(const biglong& rhs) {
		for (int i = 0; i < max_parts - 1; ++i) {
			parts[i] += rhs.parts[i];
			if (parts[i] >= max_part_value) {
				parts[i] -= max_part_value;
				++parts[i + 1];
			}
		}
		parts[max_parts - 1] += rhs.parts[max_parts - 1];
		if (parts[max_parts - 1] >= max_part_value) {
			throw std::overflow_error("biglong overflow");
		}
		return *this;
	}
	std::string c_str() const {
		std::string result;
		for (int i = max_parts - 1; i >= 0; --i) {
			if (!result.empty() || parts[i] != 0) {
				char buff[12] = {};
				if (result.empty()) {
					sprintf(buff, "%lu", parts[i]);
				} else {
					sprintf(buff, "%0*lu", part_digits, parts[i]);
				}
				result += buff;
			}
		}
		if (result.empty()) {
			result = "0";
		}
		return result;
	}
};

biglong operator+(const biglong& lhs, const biglong& rhs)
{
	return biglong(lhs) += rhs;
}

std::ostream& operator<<(std::ostream& os, const biglong& value)
{
	return os << value.c_str();
}

int main()
{
	int count = 0;
	std::cin >> count;
	for (int i = 0; i < count; ++i) {
		std::string input1, input2;
		std::cin >> input1 >> input2;
		try {
			biglong value1(input1);
			biglong value2(input2);
			biglong sum = value1 + value2;
			std::cout << sum << std::endl;
		}
		catch (const std::overflow_error&) {
			std::cout << "overflow" << std::endl;
		}
	}
	return 0;
}