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,i,j;
  string a,b;
  int sum[110]={};
  int up = 0;
  cin >> n;
  for(i=0;i<n;i++){
    cin >> a >> b;
    int sa=a.size(),sb=b.size();
    for(j=0;j<max(sa,sb);j++){
      if(sa>j&&sb>j){
	sum[j] = (a[sa-j-1]-'0') + (b[sb-j-1]-'0') + up;
      }else if(sa>j){
	sum[j] = (a[sa-j-1]-'0') + up;
      }else if(sb>j){
	sum[j] = (b[sb-j-1]-'0') + up;
      }
      up=0;
      if(sum[j]>9){
	up=1;
	sum[j]-=10;
      }
    }
    sum[max(sa,sb)]=up;
    int k=110-1;
    while(sum[k]==0&&k>0) k--;
    if(k>=80) cout << "overflow";
    else
    for(j=k;j>=0;j--)
      cout << sum[j];
    cout << endl;
  }
}

C++: #include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <queue>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <complex>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>
#include <stdio.h>

using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<double> VEC;
typedef vector<VEC> MAT;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
//container util

//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define MT(a,b,c) MP(a, MP(b, c))
#define T1 first
#define T2 second.first
#define T3 second.second.first
#define T4 second.second.second

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define EPS 1.0e-9

inline int getnum(string s, int idx){
	if(idx >= s.size())return 0;
	else return s[idx]-'0';
}

string add(string s, string t){
	reverse(ALL(s));
	reverse(ALL(t));
	int n=max(s.length(), t.length());
	string r;
	int ku=0;
	REP(i,n){
		int tmp = getnum(s, i)+getnum(t,i)+ku;
		r.PB(tmp%10+'0');
		if(tmp>9)ku=1;
		else ku=0;
	}
	if(ku)r.PB('1');
	reverse(ALL(r));
	return r;
}

int main(){
	int t;
	cin >> t;
	REP(i,t){
		string s1,s2;
		cin>>s1>>s2;
		cout << add(s1,s2) << endl;
	}

	return 0;
}

C++: #include<iostream>
#include<string>
using namespace std;
int main() {
  string a,b,c="",res;
  int n,l=0,d=0,carry=0;
  bool flag;

  cin>>n;
  for(int i=0;i<n;i++){
    cin>>a>>b;

    if(a.length() > 80 || b.length() > 80) {
      cout<<"overflow"<<"\n";
      goto NEXT;
    }

    l = min(a.length(),b.length());
    flag = a.length() > b.length();
    d=0;
    carry=0;

    for(int i=0; i<l; i++){
      d = a.at(a.length()-i-1) + b.at(b.length()-i-1) - 96 + carry;
      carry=0;
      if(d>9) {
	carry = d/10;
	d %= 10;
      }
      c+=string( 1, d+48 );
    }

    if(flag){
      for(int i=l;i<a.length(); i++){
	d = a.at(a.length()-i-1) -48 + carry;
	carry=0;
	if(d>9){
	  carry = d/10;
	  d %= 10;
	}
	c+= string( 1, d+48 );
      }
    } else {
      for(int i=l;i<b.length(); i++){
	d = b.at(b.length()-i-1) -48 + carry;
	carry=0;
	if(d>9){
	  carry = d/10;
	  d %= 10;
	}
	c+= string( 1, d+48 );
      }
    }

    if(carry) c+= string ( 1, '1' );

    res = string(c.rbegin(),c.rend());

    if(res.length() >80) {
      cout<<"overflow"<<endl;
      goto NEXT;
    }

    cout<<res<<endl;

  NEXT:
    res="";
    c="";
  }
}