Go: package main

import (
	"bufio"
	"fmt"
	"math/big"
	"os"
	"strconv"
)

var sc = bufio.NewScanner(os.Stdin)

func main() {
	sc.Scan()
	dataset, _ := strconv.Atoi(sc.Text())
	var firstdata *big.Int

	for i := 0; i < dataset*2; i++ {
		n := new(big.Int)
		sc.Scan()
		data, _ := n.SetString(sc.Text(), 10)

		if i%2 == 0 {
			firstdata = data
			continue
		}

		result := new(big.Int)
		if result := result.Add(data, firstdata); len(result.String()) > 80 {
			fmt.Println("overflow")
			continue
		} else {
			fmt.Println(result)
		}
	}
}

C++: #include <iostream>
#include <cstdlib>
using namespace std;

int main(){


  string strx,stry;
  int N;
  cin >> N;
  while(N){

    cin >> strx ;
    cin >> stry;
    int x[30] = {0},y[30] = {0};
    int i,lenx = strx.size(), leny = stry.size();
    string tmp;
    
    for( i = 0; lenx > 5 ; i++){
      tmp = strx.substr(lenx - 5);
      x[i] = atoi(tmp.c_str());
      strx =  strx.substr(0,lenx - 5);
      lenx -= 5;
    }
    x[i] = atoi(strx.c_str());
    for( i = 0; leny > 5 ; i++){
      tmp = stry.substr(leny - 5);
      y[i] = atoi(tmp.c_str());
      stry =  stry.substr(0,leny - 5);
      leny -= 5;
    }
    y[i] = atoi(stry.c_str());
    
    
    int ans[20] = {0};
    for(i = 0 ; i < 20 ; i++){
      ans[i] += x[i] + y[i];
      if(ans[i] > 99999){
	ans[i+1] += 1;
	ans[i] -= 100000;
      }
    }
    if(ans[16] != 0)
      cout << "overflow"<< endl;
    else{
      for(i = 15; i >= 0 ; i--){
	if(ans[i] != 0)
	  break;
      }
      cout << ans[i];
      for(i = i-1; i >= 0 ; i--){
	if(ans[i] < 10) cout << "0";
	if(ans[i] < 100) cout << "0";
	if(ans[i] < 1000) cout << "0";
	if(ans[i] < 10000) cout << "0";
	cout << ans[i];
      }
      cout << endl;
    }
    N--;
  }
  return 0;
}

C++: #include<iostream>
#include<string>
#include<vector>
using namespace std;

int main()
{
	int n;
	cin >> n;

	for(int i=0;i<n;++i){
		string N1,N2;
		vector<int> num_line;
		cin >> N1 >> N2;

		int upper=0;
		int num;
		string longer  = N1.size() > N2.size() ? N1 : N2;
		string shorter = N1.size() < N2.size() ? N1 : N2;

		for(int i=0;i<longer.size();++i){
			if(i < shorter.size())
				num = longer[i]-'0' + shorter[i]-'0' + upper;
			else
				num = longer[i] - '0' + upper;
			
			if(num > 9){
				upper = 1;
				if(i != longer.size() -1)
					num -= 10;
			}else{
				upper = 0;
			}

			num_line.push_back(num);
		}

		if(num_line.size() > 80)
			cout << "overflow" << endl;
		else
			for(int i = num_line.size()-1;i>=0;--i)
				cout << num_line[i] ;

	}
	return 0;
}

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

int main()
{
    int N,j;
    cin >> N;
    for(int i=0 ; i<N ; i++){
        int ans[81]={0};
        ans[0]=11111;
        char strA[100],strB[100];
        cin >> strA >> strB;
        if(strlen(strA)>80||strlen(strB)>80){
            cout << "overflow" << endl;
            break;
        }
        char str1[strlen(strA)][2],str2[strlen(strB)][2];
        for(int i=0 ; i<strlen(strA) ; i++){
            str1[i][0]=strA[i];
            str1[i][1]='\0';
        }
        for(int i=0 ; i<strlen(strB) ; i++){
            str2[i][0]=strB[i];
            str2[i][1]='\0';
        }
        int a[81]={0},b[81]={0};
        a[0]=11111;
        b[0]=11111;
        j=strlen(strA)-1;
        for(int i=80 ; j>=0 ; i--){
            a[i]=atoi(str1[j]);
            j--;
        }
        j=strlen(strB)-1;
        for(int i=80 ; j>=0 ; i--){
            b[i]=atoi(str2[j]);
            j--;
        }
        for(int i=80 ; i!=0 ; i--){
            ans[i]=ans[i]+a[i]+b[i];
            if(ans[i]>=10){
                ans[i]=ans[i]-10;
                ans[i-1]++;
            }
        }
        if(ans[0]!=11111){
            cout << "overflow" << endl;
            break;
        }
        for(int i=1 ; i<81 ; i++){
            if(ans[i]!=0){
                j=i;
                break;
            }
        }
        for(int i=j ; i<81 ; i++){
         cout << ans[i];
        }
        cout << '\n';
    }
    return 0;
}

C++: #include<iostream>
#include<queue>
#include<string>
#include<stack>
#include<cstdio>
#include<algorithm>

using namespace std;

int main(void)
{
  int n=0;
  string as;
  string bs;
  int a[100]={};
  int b[100]={};
  int c[100]={};
  int i=0;
  int alen=0;
  int blen=0;
  int clen=0;
  int k=0;
  int j=0;

  cin>>n;

  for(j=0;j<n;j++)
    {
      for(i=0;i<100;i++)
        a[i]=b[i]=c[i]=0;
      alen=0;
      blen=0;
      clen=0;
      k=0;

      cin>>as;
      cin>>bs;

      alen=as.size();
      blen=bs.size();

      for(i=0;i<alen;i++)
        {
          a[i]=as[alen-i-1];
          //printf("a[%d]=%d\n", i, a[i]);                                      
          switch(a[i])
            {
            case '0' : a[i]=0; break;
            case '1' : a[i]=1; break;
            case '2' : a[i]=2; break;
            case '3' : a[i]=3; break;
            case '4' : a[i]=4; break;
            case '5' : a[i]=5; break;
            case '6' : a[i]=6; break;
            case '7' : a[i]=7; break;
            case '8' : a[i]=8; break;
            case '9' : a[i]=9; break;
            }
        }

      for(i=0;i<blen;i++)
        {
          b[i]=bs[blen-i-1];
          //printf("b[%d]=%d\n", i, b[i]);                                      
          switch(b[i])
            {
            case '0' : b[i]=0; break;
            case '1' : b[i]=1; break;
            case '2' : b[i]=2; break;
            case '3' : b[i]=3; break;
            case '4' : b[i]=4; break;
            case '5' : b[i]=5; break;
            case '6' : b[i]=6; break;
            case '7' : b[i]=7; break;
            case '8' : b[i]=8; break;
            case '9' : b[i]=9; break;
            }
        }

      clen=(alen > blen)? alen : blen;

      for(i=0;i<clen;i++)
        {
          c[i]+=a[i]+b[i];
          c[i+1]=c[i]/10;
          if(c[clen]!=0)
            k=1;
          c[i]=c[i]%10;
        }

      if(clen>80 || c[80]!=0)
        cout<<"overflow"<<endl;

      else
        {
          for(i=clen+k-1;i>=0;i--)
            cout<<c[i];
          puts("");
        }
    }

}

C++: #include<iostream>
#include<string>
using namespace std;
int main(){
  int n;
  cin >>n;
  while(n--){
    string a,b,ans;
    cin >>a>>b;
    int as = a.size(), bs = b.size(), ms = (as>bs)? as:bs,t=0;
    for(int i=0; i<ms; i++){
      if(i<as && i<bs){t = a[as-i-1]+b[bs-i-1]+t/10-2*'0';}
      else if(i<as){t = a[as-i-1]+t/10-'0';}
      else if(i<bs){t = b[bs-i-1]+t/10-'0';}
      ans+=(char)(t%10)+'0';
    }
    if(t/10){ans+='1';}
    if(ans.size()>80){cout <<"over flow"<<endl;}
    else{for(int i=0; i<ans.size(); i++){cout <<ans[ans.size()-i-1];}cout <<endl;}
  }
  return 0;
}

C++: #include <iostream>
#include <cmath>
#include <cstdlib>

using namespace std;

int main(){
	int N; cin >> N;
	for(int i = 0; i < N; i++){
		long double a, b;
		cin >> a >> b;
		if(log10(a + b) + 1 > 80){
			cout << "overflow" << endl; 
		}
		cout << a + b << endl;
	}
	return 0;
}