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++: /*
C++ ???????????????????????????????????¬??????
??????AOJ-ITP1??????????????????
*/
#define _USE_MATH_DEFINES

#include <iostream> // ?¨??????\??????
#include <fstream>  // ??????????????\??????
#include <string>   // ???????????¢???
#include <vector>   // ???????????????
#include <cmath>    // ??°??????
#include <iomanip>  // stream???????????¢???
#include <algorithm>// max??¢??°??????

using std::cin;
using std::cout;
using std::endl;
using std::string;
using std::vector;        // ????´???°????????????????????????
using std::fixed;         // ???????????????????¨???????????????????????????????
using std::setprecision;  // ?????°????°???°?????\???????????°????????????????????¨????????\???
using std::stoi;

// ?¨??????¨?????¢??°
string calc(string str1, string str2) {
	string res;
	// ???????????????
	reverse(str1.begin(), str1.end());
	reverse(str2.begin(), str2.end());
	
	// ?????°???????????????
	while (str1.size() < str2.size())
	{
		str1 += '0';
	}
	while (str1.size() > str2.size())
	{
		str2 += '0';
	}
	int c = 0;
	// 1????????¨????¨?????????????
	for (size_t i = 0; i < str1.size(); i++)
	{
		c = c + (str1[i] - '0') + (str2[i] - '0');
		res += c % 10;
		c = c / 10;
	}

	// ?????°?????????
	if (c != 0)res += c + '0';
	if (res.size() > 80) return "overflow";
	reverse(res.begin(), res.end());
	return res;
	
}


int main() {
	int num;
	string a;
	string b;
	vector<int> aa, bb;
	cin >> num;
	for (size_t i = 0; i < num; i++)
	{
		cin >> a >> b;
		cout << calc(a, b) << endl;
	}

	return 0;
}

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

using namespace std;

#define REP(i,a,b) for((i)=(a);(i)<(int)(b);(i)++)
#define rep(i,n) REP(i,0,n)
// BEGIN CUT HERE
#define foreach(c,itr) for(typeof((c).begin()) itr=(c).begin();itr!=(c).end();itr++)
template<class T> inline string toString(T x){ostringstream sout;sout<<x;return sout.str();}
// END CUT HERE

int main(){
  int i, j, n;

  cin >> n;
  rep(i,n){
    string str1, str2, res;
    cin >> str1;
    cin >> str2;

    vector<int> a(80, 0);
    rep(j,str1.length()) a[j] = str1[str1.length()-1-j] - '0';

    vector<int> b(80, 0);
    rep(j,str2.length()) b[j] = str2[str2.length()-1-j] - '0';

    rep(j,80){
      int sum = a[j] + b[j];
      if(sum >= 10){ sum %= 10; a[j+1]++;}
      res += sum + '0';
    }

    reverse(res.begin(), res.end());
    bool f = false;
    rep(j,res.length()){
      if(res[j] != '0') f = true;
      if(f) printf("%c", res[j]);
    }
    printf("\n");
  }

  return 0;
}

C++: #include<iostream>
#include<stdio.h>
#include <algorithm>
#include <utility>
using namespace std;
using namespace std;
int main(){
	
	int m;
	char in[2][10000];
	char ans[100000];
	int ie[2];
	//
	int ien[2];
	bool max10;
	int Min;
	bool NMin;
	//
	scanf("%d",&m);
	m=1;
	for(;m--;){
		
		for(int i=0;i<2;i++){
			scanf(" %s",&in[i]);
		}
		for(int i=0;i<2;i++){
			for(ie[i]=0;in[i][ie[i]]!='\0';ie[i]++){
				in[i][ie[i]]=in[i][ie[i]]-'0';
			}
		}
		ie[0]--;
		ie[1]--;
		Min=max(ie[0],ie[1]);
		if((Min>79)||(Min>78)&&(in[0][0]+in[1][0]>9)){
			cout<<"overflow"<<endl;
		}else{	
			if(ie[0]>ie[1]){
				NMin=0;
			}else{
				NMin=1;
			}
			ien[0]=ie[0];
			ien[1]=ie[1];
			for(;min(ien[0],ien[1])+1;ien[0]--,ien[1]--){
				in[NMin][ien[NMin]]=in[0][ien[0]]+in[1][ien[1]];
				cout<<int(in[NMin][ien[NMin]])<<endl;
				if(in[NMin][ien[NMin]+1]>9){
					in[NMin][ien[NMin]+1]-=10;
					in[NMin][ien[NMin]]  +=1;
				}
				
			}
			max10=0;
			if(in[NMin][ien[NMin]+1]>9){
				in[NMin][ien[NMin]+1]-=10;
				max10=1;
			}
			for(int i=0;i<2;i++){
				for(int j=0;j<ie[i]+1;j++){
					in[i][j]=in[i][j]+'0';
				}
			}
			if(max10) cout<<"1";
			cout<<in[NMin]<<endl;
		}
	}
	return 0;
}

C++: #include <iostream>
#include <string>
#include <stdlib.h>
using namespace std;


int getValue(string str, int i){
	int endp,startp;

	endp = str.length() - 8 * i;
	startp = str.length() - 8 - 8 * i;
	if( endp <= 0 )
		return 0;
	else if( startp <= 0 ) {
		return atoi( str.substr(0,endp).c_str() );					
	}
	else {
		return atoi( str.substr(startp,8).c_str() );					
	}
	return -1;
}


int main()
{
	int num,i,j,startp,endp;
	string str1, str2;
	long v1,v2;
	int v[10];
	cin >> num;
	for(i = 0; i < num; i++ ) {
		cin >> str1;
		cin >> str2;
		if( str1.length() > 80 || str2.length() > 80 ){
			
		}
		//8桁ずつ分けて計算
		int flg = 0;
		for( j = 0; j < 10; j++ ) {
			v1 = getValue( str1, j );
			v2 = getValue( str2, j );
			
			v[j] = v1 + v2 + flg;
			if( v[j] >= 100000000 ) {
				flg = 1;
				v[j] -= 100000000;
			}
			else {
				flg = 0;
			}
		}
		if( flg == 1 )
			printf("overflow\n");
		else {
			flg = 0;
			for( i = 9 ; i >= 0; i-- ) {
				if( v[i] > 0 ){
					printf("%d",v[i] );
					flg = 1;
				}
				else if( flg == 1 ) {
					printf("%08d",v[i] );
				}
				
			}
			printf("\n");	
		}
	}




	return 0;
}