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>
#include<vector>
#include<algorithm>
#include<cstdlib>
using namespace std;
typedef long long int ll;

int main()
{
	int n;
	cin >> n;
	for(int i=0;i<n;i++){
		int a[80];
		string sa1,sa2,s1="",s2="";
		for(int i=0;i<80;i++)a[i]=0;
		cin >> sa1 >> sa2;
		for(int j=0;j<80-sa1.length();j++){
			s1+='0';
		}
		s1+=sa1;
		for(int j=0;j<80-sa2.length();j++){
			s2+='0';
		}
		s2+=sa2;
		for(int i=0;i<80;i++){
			a[i]+=(s1[i]-'0')+(s2[i]-'0');
		}
		for(int i=79;i>=1;i--){
			a[i-1]+=a[i]/10;
			a[i]%=10;
		}
		if(a[0]>=10){
			printf("overflow\n");
			continue;
		}
		int x=0;
		while(a[x]==0)x++;
		for(int i=x;i<=79;i++){
			cout << a[i];
		}
		if(x==80)printf("0\n");
		else printf("\n");
	}
    return 0;
}

C++: #include "bits/stdc++.h"

#define debug(x) cout<<#x<<": "<<x<<endl
#define rep(i,n) for (int i=0;i<(n);i++)
#define FOR(i,a,b) for (int i=(a);i<=(b);i++)
#define all(a) (a).begin(),(a).end()
using namespace std;
typedef vector<int> VI;
typedef vector<vector<int>> VVI;
typedef long long ll;
ll gcd(ll a, ll b) {
	ll c;
	while (a != 0) {
		c = a; a = b%a;  b = c;
	}
	return b;
}

void solve() {
#ifdef _WIN32
	istream &cin = ifstream("input.txt");
#endif
	int n;
	cin >> n;
	rep(i, n) {
		vector<ll> v1(11), v2(11);
		string s1, s2;
		cin >> s1 >> s2;
		rep(j, 10) {
			if (s1.size() > 10 * j) v1[j] = stoi(s1.substr(10 * j, min(10u, s1.size() - 10 * j)));
			if (s2.size() > 10 * j) v2[j] = stoi(s2.substr(10 * j, min(10u, s2.size() - 10 * j)));
		}
		rep(j, 11) {
			v1[j] += v2[j];
			if (v1[j] >= 1e10) {
				v1[j] -= 1e10;
				v2[j]++;
			}
		}
		if (v1[8] || v1[9] || v1[10]) cout << "overflow" << endl;
		else {
			rep(j, 11) if (v1[10 - j] != 0) cout << v1[10 - j];
			cout << endl;
		}
	}

}




int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);


	solve();
	system("PAUSE");
	return 0;
}

C++: #include<iostream>
#include<string>
#include<algorithm>
using namespace std;
int main(){
	string a,b,c;
	int n;
	cin>>n;
	for(int fjal=0;fjal<n;fjal++){
	cin>>a>>b;
	c.clear();
	if(a.size()<b.size())swap(a,b);
	int as=a.size();
	while(as!=b.size())b="0"+b;
	//cout<<a<<" "<<b;
	bool kuri=false;
	for(int i=as-1;i>=0;i--){
		int _a=a[i]-'0',_b=b[i]-'0',ans=_a+_b;
		if(kuri)ans++;
		if(ans>=10){
			kuri=true;
			ans-=10;
		}
		else {kuri=false;}
		c.push_back(ans+'0');
	}
		if(kuri)c.push_back('1');
	
		if(c.size()<80){for(int i=c.size()-1;i>=0;i--)cout<<c[i];
		cout<<endl;
		}
		else cout<<"overfllow"<<endl;
	}
	return 0;
}

C++: #include <stdio.h>
#include <iostream>
#include <algorithm>
#include <string>

using namespace std;

string hissan(string a, string b) {
    if (a.size() < b.size()) a.swap(b);
    int bi = b.size() - 1;
    int c = 0;
    string ans;

    for (int i = a.size() - 1; i >= 0; i--) {
        int _a = a[i] - '0';
        int _b = (bi >= 0) ? b[bi--] - '0' : 0;
        int x = _a + _b + c;

        if (x < 10) {
            c = 0;
        }
        else {
            x -= 10;
            c = 1;
        }
        ans.insert(0, to_string(x));
    }

    if (c) ans.insert(0, "1");

    return ans;
}

int main()
{
    int n;
    string a, b;

    cin >> n;
    while(n--) {
        cin >> a;
        cin >> b;
        string x = hissan(a, b);
        cout << ((x.size() > 80) ? "overflow" : x) << endl;
    }
    return 0;
}