Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

func main() {
	scanner.Split(bufio.ScanWords)

	const maxCapacity = 512 * 1024
	buf := make([]byte, maxCapacity)
	scanner.Buffer(buf, maxCapacity)

	n := nextInt()
	maxint, _ := new(big.Int).SetString("100000000000000000000000000000000000000000000000000000000000000000000000000000000", 10)

	for i := 0; i < n; i++ {
		aStr := nextString()
		bStr := nextString()

		a, _ := new(big.Int).SetString(aStr, 10)
		b, _ := new(big.Int).SetString(bStr, 10)
		c := big.NewInt(0).Add(a, b)

		if c.Cmp(maxint) < 0 {
			fmt.Println(c)
		} else {
			fmt.Println("overflow")
		}
	}
}

C++: #include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <ctime>
#include <cstring>
#include <climits>
#include <algorithm>
#include <map>
#include <set>
#include <stack>
#include <vector>
#include <queue>
#include <string>
#include <complex>
using namespace std;

#define rep(i,n) for(int i=0; i<n; i++)
#define repa(i,s,e) for(int i=s; i<=e; i++)
#define repd(i,s,e) for(int i=s; i>=e; i--)

typedef vector<int> vi;

int n;
string s1, s2;
char n1[81], n2[81], sum[81];

int main() {
	scanf("%d", &n);
	rep(i,n) {
		memset(n1, 0, sizeof(n1));
		memset(n2, 0, sizeof(n2));
		memset(sum, 0, sizeof(sum));

		cin>>s1>>s2;
		int l1 = s1.size();
		int l2 = s2.size();
		if(max(l1,l2) > 80) {
			printf("overflow\n");
			return 0;
		}

		rep(k,l1) n1[k] = s1[l1-k-1] - '0';
		rep(k,l2) n2[k] = s2[l2-k-1] - '0';

		char a = 0;
		rep(i,80) {
			char c = n1[i] + n2[i] + a;
			a = c / 10;
			sum[i] = c % 10;
		}

		if(sum[80] != 0) {
			printf("overflow\n");
			return 0;
		}

		bool start = false;
		repd(i,80,0) {
			if(sum[i] != 0) start = true;
			if(!start && sum[i] == 0) continue;
			printf("%d", sum[i]);
		}
		if(!start) printf("0");
		printf("\n");
	}
}

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

using namespace std;

string sum(string& a, string& b){
	int i = a.length() - 1;
	int j = b.length() - 1;
	int carry = 0;
	string temp;

	while(i >= 0 || j >= 0){
		int c = i >= 0 ? a[i] - '0' : 0;
		int d = j >= 0 ? b[j] - '0' : 0;

		temp.push_back((c + d + carry) % 10 + '0');
		carry = (c+d) / 10;
		--i, --j;
	}

	if(carry)
		temp.push_back('1');

	reverse(begin(temp), end(temp));

	return temp;
}

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

	vector<string> input(n*2);

	for(int i = 0; i < n*2; i++){
		cin >> input[i];
	}

	for(int i = 0; i < n; i++){
		string t = sum(input[2*i], input[2*i+1]);
		if(t.size() <= 80)
			cout << t << endl;
		else
			cout << "overflow" << endl;
	}

	return 0;
}

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

int main(){

  std::string num1("10000");
  std::string num2("990000");
  int n;

  //std::cin >> n;
  n=1;

  for(int i=0;i<n;i++){
    //std::cin >> num1 >> num2;
    if(num1.size()<num2.size()){
      num1.swap(num2);
    }
    std::cout << num1 << std::endl;
    std::cout << num2 << std::endl;
  }
}

C++: #include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(void)
{
	char num1[1002],num2[1002];
	int a1[1002],a2[1002],ans[1002];
	int i,j,n,k,l1,l2,kuriagari=0;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		kuriagari=0;
		for(j=0;j<1002;j++)
		{
			num1[j]='\0';
			num2[j]='\0';
			a1[j] = 0;
			a2[j] = 0;
			ans[j] = 0;
		}
		scanf("%s",num1);
		scanf("%s",num2);
		l1 = strlen(num1);
		l2 = strlen(num2);
		for(j=0;j<l1;j++)
		{
			a1[j] = num1[l1-1-j] - '0';
		}
		for(j=0;j<l2;j++)
		{
			a2[j] = num2[l2-1-j] - '0';
		}
		for(j=0;j<1002;j++)
		{
			ans[j] = (a1[j] + a2[j] + kuriagari) % 10;
			if((int)((a1[j] + a2[j] + kuriagari)/10) == 1)
			{
				kuriagari = 1;
			}
			else
			{
				kuriagari = 0;
			}
		}
		if(ans[1000] != 0)
		{
			printf("overflow\n");
		}
		else
		{
			for(j=1001;j>=0;j--)
			{
				if(ans[j] != 0)
				{
					k = j;
					break;
				}
			}
			for(j=k;j>=0;j--)
			{
				printf("%d",ans[j]);
			}
			printf("\n");
		}
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <stack>

using namespace std;

int main(void){
	stack <char> buffer;
	int a[80],n,i,j;
	char buffer2;
	cin >> n;
	scanf(" ");
	for (int i = 0; i < n; i++)
	{
		for(j=0;j<80;j++) a[j]=0;
		while(1){
			scanf("%c",&buffer2);
			if(buffer2=='\n') break;
			buffer.push(buffer2);
		}
		buffer2 = 0;
		for(j=0;!buffer.empty();j++){
			a[j]+=buffer.top()-'0';
			buffer.pop();
		}
		while(1){
			scanf("%c",&buffer2);
			if(buffer2=='\n') break;
			buffer.push(buffer2);
		}
		buffer2 = 0;
		for(j=0;!buffer.empty();j++){
			a[j]+=buffer.top()-'0';
			buffer.pop();
		}
		for(j=0;a[j]!=0;j++){
			if(a[j]>=10){
				if(j==79) goto error;
				a[j]-=10;a[j+1]++;
			}
		}
		for(j=79;a[j]==0;j--);
		for(;j>=0;j--){
			cout << a[j];
		}
		error:	cout << endl;
	}
	return 0;
}

C++: #include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(void)
{
	char num1[82],num2[82];
	int a1[82],a2[82],ans[82];
	int i,j,n,k,l1,l2,kuriagari=0;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		for(j=0;j<82;j++)
		{
			a1[j] = 0;
			a2[j] = 0;
			ans[j] = 0;
		}
		scanf("%s",num1);
		scanf("%s",num2);
		l1 = strlen(num1);
		l2 = strlen(num2);
		for(j=0;j<l1;j++)
		{
			a1[j] = num1[l1-1-j] - '0';
		}
		for(j=0;j<l2;j++)
		{
			a2[j] = num2[l2-1-j] - '0';
		}
		for(j=0;j<82;j++)
		{
			ans[j] = (a1[j] + a2[j] + kuriagari) % 10;
			if((int)((a1[j] + a2[j] + kuriagari)/10) == 1)
			{
				kuriagari = 1;
			}
			else
			{
				kuriagari = 0;
			}
		}
		if(ans[80] != 0)
		{
			printf("overflow\n");
		}
		else
		{
			for(j=81;j>=0;j--)
			{
				if(ans[j] != 0)
				{
					k = j;
					break;
				}
			}
			for(j=k;j>=0;j--)
			{
				printf("%d",ans[j]);
			}
			printf("\n");
		}
	}
	return 0;
}

C++: #include<cstdio>
#include<cmath>
#include<iostream>
#include<algorithm>
#include<queue>
using namespace std;
int main(){
    int n;
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        string a,b;
        int aa[81]={0},bb[81]={0};
        cin>>a>>b;
        for(int j=a.size()-1,jj=80;0<=j;j--,jj--)
            aa[jj]=a[j]-'0';
        for(int j=b.size()-1,jj=80;0<=j;j--,jj--)
            bb[jj]=b[j]-'0';
        for(int j=80;0<j;j--){
            aa[j]+=bb[j];
            aa[j-1]+=aa[j]/10,aa[j]=aa[j]%10;
        }
        if(aa[0])puts("overflow");
        else{
            int j=0;
            for(;;j++)
                if(aa[j])break;
            for(int k=j;k<=80;k++)
                printf("%d",aa[k]);
            puts("");
        }
    }
    return 0;
}

C++: #include<iostream>

using namespace std;


string solve(string s1, string s2){

while(s1.size()<85){
s1 = '0' + s1;
}
while(s2.size()<85){
s2 = '0' + s2;
}
string ret = "";
int kuri = 0;
for(int i=0;i<80;i++){
int r = (int)(s1[s1.size()-1-i]-'0' + s2[s2.size()-1-i]-'0') + kuri;
kuri = r/10;
r = r%10;
ret = ((char)('0'+r)) + ret;
}
if (kuri>0) return "overflow"; else return ret;
}

int main(void){
int N;
cin >> N;
for(int i=0i<N;i++){
string s1, s2;
cin >> s1 >> s2;
cout << solve(s1, s2) << endl;
}
return 0;
}

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

string solve(string s1, string s2){
while(s1.size()<100){
s1 = '0' + s1;
}
while(s2.size()<100){
s2 = '0' + s2;
}
string ret = "";
int kuri = 0;
for(int i=0;i<80;i++){
int r = (int)(s1[s1.size()-1-i]-'0') + (int)(s2[s2.size()-1-i]-'0') + kuri;
kuri = r/10;
r = r%10;
ret = ((char)('0'+r)) + ret;
}
if (kuri>0) return "overflow";
else{
string ret2 = "0";
for(int i=0;i<ret.size();i++){
if (ret[i]!='0'){ret2 = ret.substr(i);break;}
}
return ret2;
}
}

int main(void){
int N;
cin >> N;
for(int i=0;i<N;i++){
string s1, s2;
cin >> s1;
cin >> s2;
cout << solve(s1, s2) << endl;
}
return 0;
}