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>
using namespace std;

int main()
{
	int n;
	cin >> n;
	for (int i = 0; i < n; ++i)
	{
		int A[150] = {},B[150] = {},C[150] = {};
		string inA,inB;
		cin >> inA >> inB;
		for (int j = 0; j < inA.size(); ++j)
			A[inA.size()-j] = (int)(inA[j]-'0');
		for (int j = 0; j < inB.size(); ++j)
			B[inB.size()-j] = (int)(inB[j]-'0');
		for (int j = 1; j < 150; ++j)
		{
			C[j] += A[j] + B[j];
			if(C[j] >= 10)
			{
				C[j+1] += C[j]/10;
				C[j] = C[j]%10;
			}
		}
		if(C[80] != 0)
		{
			cout << "overflow" << endl;
			continue;
		}
		else
		{
			bool haji = 0;
			for (int j = 149; j > 0; --j)
			{
				if(C[j] != 0)
					haji = 1;
				if(haji)
				{
					cout << C[j];
				}
			}
			cout << endl;
		}
	}
}

C++: #include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <algorithm>
#include <functional>

using namespace std;

class lInt
{
private:
	vector<int> place;
public:
	lInt( string number )
	{
		for ( unsigned int i = 0; i < number.length(); i++ )
		{
			place.push_back( number[i] - '0' );
		}

		reverse( place.begin(), place.end() );

		return;
	}

	void printNumber()
	{
		if ( place.size() < 80 )
		{
			for ( vector<int>::reverse_iterator it = place.rbegin(); it != place.rend(); it++ )
			{
				cout << *it;
			}
		}
		else
		{
			cout << "overflow";
		}

		cout << endl;

		return;
	}

	void operator += ( string number )
	{
		vector<int> buffer;
		
		for ( unsigned int i = 0; i < number.length(); i++ )
		{
			buffer.push_back( number[i] - '0' );
		}
		reverse( buffer.begin(), buffer.end() );

		for ( unsigned int i = 0; i < buffer.size(); i++ )
		{
			if ( i < place.size() )
			{
				place[i] += buffer[i];
			}
			else
			{
				place.push_back( buffer[i] );
			}
		}
		
		for ( unsigned int i = 0; i < place.size(); i++ )
		{
			if ( 10 <= place[i] )
			{
				if ( i + 1 < place.size() )
				{
					place[i + 1] += place[i] / 10;
				}
				else
				{
					place.push_back( place[i] / 10 );
				}

				place[i] %= 10;
			}
		}
	}
};

int main()
{
	int n;
	string buffer;

	cin >> n;

	for ( int i = 0; i < n; i++ )
	{
		cin >> buffer;
		lInt li( buffer );

		cin >> buffer;
		li += buffer;

		li.printNumber();
	}

	return 0;
}

C++: //RE
#include<iostream>
#include<algorithm>
#include<vector>
#include<queue>
#include<deque>
#include<map>
#include<set>
#include<string>
#include<sstream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<cctype>
#include<climits>
using namespace std;
#define REP(i, j) for(int i = 0; i < j; i++)
#define FOR(i, j, k) for(int i = j; i < k; i++)
#define P pair<int, int>
const int INF = INT_MAX / 2;
const int N = 100;

vector<int> makeDx(string str){
    reverse(str.begin(), str.end());
    vector<int> ret(N, 0);
    REP(i, str.size()) ret[i] = str[i] - '0';
    return ret;
}

bool isOver80(vector<int> dx){
    FOR(i, 80, dx.size()) if(dx[i] != 0) return true;
    return false;
}

int main(){
    int n; cin >>n;
    REP(z, n){
        string str[2]; cin >>str[0] >>str[1];
        if(str[0].size() > 80 || str[1].size() > 80){
            cout <<"overflow" <<endl;
            continue;
        }

        vector<int> dx[2] = {makeDx(str[0]), makeDx(str[1])};
        vector<int> ans(N, 0);

        REP(i, max(dx[0].size(), dx[1].size())){
            ans[i] += (dx[0][i] + dx[1][i]);
            ans[i + 1] += (ans[i] / 10);
            ans[i] %= 10;
        }

        if(isOver80(ans)){
            cout <<"overflow" <<endl;
            continue;
        }

        reverse(ans.begin(), ans.end());
        int s = 0;
        while(ans[s] == 0 && s < ans.size() - 1) s++;
        //debug
        //cout <<"size = " <<ans.size() - s <<endl;
        FOR(i, s, ans.size()) cout <<ans[i];
        cout <<endl;
    }
    return 0;
}

C++: #include<iostream>
#include<stdio.h>
#include <algorithm>
#include<string>
#include <utility>
using namespace std;
using namespace std;
int main(){
	int m;
	string in,in2;
	int a[90],b[90],ans[90];
	int f;
	int a_len,b_len,m_len;
	cin>>m;
	while(m--){
		for(int i=0;i<90;i++){
			a[i]=b[i]=ans[i]=0;
		}
		cin>>in;
		cin>>in2;
		a_len=in.size();
		b_len=in2.size();
		for(int i=0;i<a_len;i++){
			a[a_len-1-i]=in[i]-'0';
		}
		for(int i=0;i<b_len;i++){
			b[b_len-1-i]=in2[i]-'0';
		}
		m_len=max(a_len,b_len);
		if(m_len>80){
			cout<<"overflow"<<endl;
			continue;
		}
		f=0;
		for(int i=0;i<m_len+1;i++){
			ans[i]=(a[i]+b[i]+f)%10;
			f=(a[i]+b[i]+f)/10;
		}
		if(ans[m_len]!=0){
			printf("%d",ans[0]);
		}
		
		
	}
	
	
	return 0;
}