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 <string.h>

using namespace std;

int main(void){
	int n;

	cin >> n;
	for(int i=0;i<n;i++){
		int len,mlen=0;
		char val[2][81]={0},tmp[81],crr=0;

		for(int j=0;j<2;j++){
			cin >> tmp;
			len = strlen(tmp);
			mlen = mlen>len?mlen:len;
			for(int k=0;k<len;k++)
				val[j][len-1-k]=tmp[k]-0x30;
		}

		for(int j=0;j<mlen;j++){
			val[0][j]+=val[1][j]+crr;
			crr=val[0][j]/10;
			val[0][j]%=10;

			if(j==mlen-1&&crr)
				mlen++;
		}

		if(!val[0][80]){
			for(int j=0;j<mlen;j++)
				tmp[j]=val[0][mlen-1-j]+0x30;
			tmp[mlen]='\0';
		}
		else
			strcpy(tmp,"overflow");

		cout << tmp << endl;
	}

	return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<sstream>
#include<string>
using namespace std;
int main(){
	int n;
	for(cin>>n;n--;){
		string a,b;
		cin>>a;
		cin>>b;
		reverse(a.begin(),a.end());
		reverse(b.begin(),b.end());
		while(a.size()<b.size())a+='0';
		while(b.size()<a.size())b+='0';
		a+='0';
		cout<<a<<endl;
		cout<<b<<endl;
		int f=0;
		for(int i=0;i<a.size()-1;i++){
			if((a[i]-'0')+(b[i]-'0')+f>9){
				a[i]=(a[i]-'0')+(b[i]-'0')+f-10;
				f=1;
			}else{
				a[i]=(a[i]-'0')+(b[i]-'0');
				f=0;
			}
			a[i]+='0';
			cout<<a[i];
		}
		cout<<endl;
		reverse(a.begin(),a.end());
		cout<<endl<<f<<endl;
		if(f)a='1'+a;
		if(a.size()>80){
			cout<<"over flow"<<endl;
		}else{
			for(int i=0;i<a.size();i++){
				if(a[i]!='0' || i!=0)
				cout<<a[i];
			}
			cout<<endl;
		}
	}
	return 0;
}

C++: //0015
#include <bits/stdc++.h>
using namespace std;

int main(){
	long n;
	cin>>n;
	while(n--){
		string a,b,ans;
		long tmp = 0,i;
		cin>>a>>b;
		while(a.size() != b.size()){
		if(a.size() > b.size()){
			while(a.size() != b.size()){
				b = '0' + b;
			}
		}

		else if(a.size() < b.size()){
			while(a.size() != b.size()){
				a = '0' + a;
			}
		}
		}

		reverse(a.begin(),a.end());
		reverse(b.begin(),b.end());

		for(i = 0;i < a.size()||i < b.size();i++){
			tmp = (int)(a[i] - '0') + (int)(b[i] - '0') + (int)tmp;
			ans = ((char)((tmp % 10)+'0')) + ans;

			tmp /= 10;
		}

		if(tmp != 0)
			ans = '1' + ans;

		if(ans.size() > 80)
			cout<<"overflow"<<endl;
		else
			cout<<ans<<endl;
	}
	return 0;
}

C++: #include <iostream>
#include <string.h>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
int main(){
  int n, maxlen;
  char a[100], b[100];

  cin >> n;
  for(int ii = 0 ; ii < n ; ii++){
    string ans = "";
    scanf("%s%s", a, b);
    
    maxlen = max(strlen(a), strlen(b));

    reverse(a, a+strlen(a));
    reverse(b, b+strlen(b));
    
    for(int i = strlen(a) ; i < 100 ; i++){
      a[i] = '0';
    }
    for(int i = strlen(b) ; i < 100 ; i++){
      b[i] = '0';
    }

    int tmp, tmp2 = 0;
    bool flag = 0;

    for(int i = 0 ; i < maxlen ; i++){
      tmp = (a[i] - '0') + (b[i] - '0') + tmp2;
      
      if(i == maxlen - 1){
	//cout << "OK" << endl;
	//tmp = (a[i] - '0') + (b[i] - '0') + tmp2;
	if(tmp >= 10){
	  tmp2 = 1;
	  tmp -= 10;
	  ans += tmp + '0';
	  ans += '1';
	}
	else ans += tmp + '0';
      }

      else if(tmp >= 10){
	tmp2 = 1;
	tmp -= 10;
	ans += tmp + '0';
      }
      else if(tmp <= 9){
	ans += tmp + '0';
	tmp2 = 0;
      }
    }

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

    cout << ans << endl;
  }
  return 0;
}

C++: #include<cstdio>
#include<algorithm>
using namespace std;
int main(void)
{
	int y;
	scanf("%d",&y);
	for(int z = 0;z < y;z++)
	{
		char suji1[82],suji2[82];
		char ans[82] = {0};

		for(int i = 0;i<82;i++)
		{
			suji1[i] = '0';
			suji2[i] ='0';
		}

		int overflow = 0;

		scanf("%s",suji1);
		scanf("%s",suji2);
		int suji1s = strlen(suji1);
		int suji2s = strlen(suji2);

		int anss;
		if(suji1s>suji2s)  anss = suji1s;
		else anss = suji2s;

		suji1[suji1s] = '0';
		suji2[suji2s] = '0';

		reverse(suji1,suji1+suji1s);
		reverse(suji2,suji2+suji2s);

		for(int i = 0;i < 80;i++)
		{
			ans[i] = suji1[i]+suji2[i] - '0';
			if(ans[i] >= ':')
			{
				ans[i]  = ans[i] - 10;
				suji2[i+1] = suji2[i+1]+1;
			}
		}
		
		if(ans[anss]!= '0') anss++;
		if(anss >=81) overflow = 1;
		reverse(ans,ans+anss);
		ans[anss] = 0;
		if(overflow >= 1)
		{
			printf("overflow\n");
		}
		else
		{
			printf("%s\n",ans);
		}
		
	}
	return 0;
}

C++: #include<algorithm>
#include<string>
#include<iostream>

using namespace std;
int main(){
	int n,l,m,c;
	string a,b;
	cin >> n;
	for(int i=0;i<n;i++){
		char s[90] = {0};
		cin >> a;
		cin >> b;
		reverse(a.begin(),a.end());
		reverse(b.begin(),b.end());
		if(a.length()<b.length())swap(a,b);
		l = a.length();
		m = b.length();
		c=0;
		for(int j=0;j<l;j++){
			int o=a[j]-'0' + c;
			if(j<m)o += b[j]-'0';
			c = o>9;
			s[j] = o%10 + '0';
		}
		if(c>0)s[l++]='1';
		reverse(s,s+l);
		if(l>80)cout << "overflow" << endl;
		else cout << s << endl;
	}
	return 0;
}

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

int main(void)
{
	char str[2][1000];
	int b, s;
	int len[2];
	int i, j;
	int n;
	int flag;
	
	scanf("%d", &n);
	
	while (n){
		for (i = 0; i < 1000; i++){
			str[0][i] = str[1][i] = 0;
		}
		s = 1;
		b = 0;
		for (i = 0; i < 2; i++){
			scanf("%s", str[i]);
			len[i] = strlen(str[i]);
		}
		
		if (len[0] > 80 || len[1] > 80){
			printf("overflow\n");
			break;
		}
		else {
			if (len[0] < len[1]){
				s = 0;
				b = 1;
			}
			
			for (i = len[b], j = len[s]; i >= 0; i--, j--){
				if (j >= 0){
					str[s][i] = str[s][j];
				}
				else {
					str[s][i] = '0';
				}
			}
			
			flag = 0;
			i = len[b];
			while (i >= 0){
				if (str[s][i] + str[b][i] - '0' + flag > '9'){
					flag = 1;
				}
				else {
					flag = 0;
				}
				i--;
			}
			
			if (flag){
				for (i = len[b]; i >= 0; i--){
					for (j = 0; j < 2; j++){
						str[j][i + 1] = str[j][i];
					}
				}
				str[0][0] = '0';
				str[1][0] = '0';
			}
			
			for (i = j = len[b]; j >= 0; i--, j--){
				str[b][i] += (str[s][j] - '0');
				if (str[b][i] > '9'){
					str[b][i] -= 10;
					str[b][i - 1]++;
				}
			}
			str[b][len[b] + flag] = '\0';
			
			printf("%s\n", str[b]);
		}
		
		n--;
	}
	
	return (0);
}

C++: #include <iostream>
#include <string>
#include <algorithm>

using namespace std;

int main(void){
	int n;

	cin >> n;
	while(n--){
		int len,big;
		string val[2];
		bool crr=false;

		for(int j=0;j<2;j++){
			cin >> val[j];
			reverse(val[j].begin(),val[j].end());
		}

		big=val[0].size()>=val[1].size()?0:1;
		val[1-big].append((len=val[big].size())-val[1-big].size(),'0');

		if(len<=80){
			for(int j=0;j<len;j++){
				val[0][j]+=val[1][j]+crr-0x60;
				crr=val[0][j]/10;
				val[0][j]%=10;
				val[0][j]+=0x30;
			}

			if(crr){
				val[0].append(1,'1');
				len++;
			}
		}

		if(len<=80)
			reverse(val[0].begin(),val[0].end());
		else
			val[0]="overflow";

		cout << val[0] << endl;
	}

	return 0;
}