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(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<cstdio>
#include<algorithm>
#include<string.h>
//#include<string>

using namespace std;

#define MAX(x,y) ((x>y)? x:y)


int n;//データセットの数

char str[2][10000];//	入力される整数文字列
int n_str[2];//長さを収納

char answer[85];

FILE *fp=stdin;

int main()
{
	fscanf(fp,"%d",&n);
	for(int i=0;i<n;i++)
	{
		sta:
		fscanf(fp,"%s%s",&str[0],&str[1]);
		for(int j=0;j<2;j++)n_str[j]=strlen(str[j]);
		int max =0,min=1;
		if(n_str[1]>n_str[0])
		{
			max=1;
			min=0;
		}
		int s = n_str[max]-n_str[min];
		char cha[10000];
		fill(cha,cha+80,'0');
		for(int j=n_str[min];j>=0;j--)
		{
			cha[j+s]=str[min][j];
		}
		strcpy(str[min],cha);
		fill(answer,answer+85,0);
		for(int j=n_str[max]-1;j>=0;j--)
		{
			answer[j]=str[0][j]+str[1][j]-'0';
			if(answer[j]>'9')//繰り上がり時の処理
			{
				answer[j]-=10;
				if(j==0)
				{
					if(n_str[max]>=80)
					{
						n_str[max]++;
					}

					else printf("1");
				}
				else str[0][j-1]++;
			}
		}
		if(n_str[max]>80)
		{
			printf("overflow\n");
		}
		else printf("%s\n",answer);
	}
	fclose(fp);
	return 0;
}

C++: #include<iostream>
#include<string>
#include<algorithm>
using namespace std;
int main(){
  int n;
  cin >>n;
  while(n--){
    string a,b;
    cin >>a>>b;
    int num[900] = {0},tab = 0,i = 0;
    int as = a.size()-1;
    int bs = b.size()-1;
    int nmi = min(as,bs);
    int nma = max(as,bs);
    for(int x; i<=nma; i++){
      if(i<=nmi){x = tab+a[as-i]+b[bs-i]-'0'*2;}
      else if(as<bs){x = tab+b[bs-i]-'0';}
      else if(bs<as){x = tab+a[as-i]-'0';}
      tab = x/10;
      num[i] = x%10;
    }
    if(tab){num[nma] = tab;i++;}
    if(i>80){cout <<"overflow";}
    else{for(int x=i-1; x>=0; x--){cout <<num[x];}}
    cout <<endl;
  }
  return 0;
}

C++: #include <stdio.h>
#include <string.h>
int main(void){
    int n,ap,bp,cp,t;
    char a[81],b[81],c[81];
    scanf("%d",&n);
    while(~scanf("%s%s",&a,&b)){
        ap=strlen(a);
        bp=strlen(b);
        cp=sizeof(c);
        c[cp]='\0';
        t=0;
        while(cp){
            t+=(ap?a[--ap]-'0':0)+(bp?b[--bp]-'0':0);
            c[--cp]='0'+(t%10);
            t/=10;
        }
        while(t) c[--cp]='0'+(t%10);
        printf("%s\n",&c[cp]);
    }
    return 0;
}

C++: #include "string.h"
#include "math.h"
#include "stdio.h"
#include <iostream>
using namespace std;

/** Problem0015 : National Budget **/
int main()
{
	string a, b, s;
	int n, tmp, la, lb;
	bool up=false;
	
	cin >> n;
	for (int i=0; i<n; i++) {
		cin >> a >> b;
		s="";
		
		reverse(a.begin(), a.end());
		reverse(b.begin(), b.end());
		la=(int)a.length();
		lb=(int)b.length();
		
		if (la < lb) {
			swap(la, lb);
			swap(a, b);
		}
		
		for (int i = 0; i<la-lb; i++) b+='0';
		
		for (int i=0; i<la; i++) {
			tmp = (a[i]-'0') + (b[i] - '0') + (up?1:0);
			if (tmp>=10) {
				s += '0'+tmp%10;
				up = true;
			} else {
				s += '0'+tmp;
				up = false;
			}
		}
		
		if (up)
			s+='1';
		reverse(s.begin(), s.end());
		if (s.length()>80)
			cout << "overflow" << endl;
		else
			cout << s << endl;
	}
	return 0;
}

C++: #include "bits/stdc++.h"
using namespace std;
int main() {
	cin.tie(0); ios::sync_with_stdio(false);
	int N; cin >> N;
	for (int i = 0; i < N;i++) {
		vector<int> v1(101), v2(101);
		string str1, str2;
		cin >> str1 >> str2;
		for (int j = 0; j < str1.size(); j++) v1[j] = str1[str1.size() - j - 1] - '0';
		for (int j = 0; j < str2.size(); j++) v2[j] = str2[str2.size() - j - 1] - '0';
		for (int j = 0; j < 100;j++) {
			v1[j] += v2[j];
			if (v1[j] >= 10) {
				v1[j] -= 10;
				v1[j + 1]++;
			}
		}
		int dig = 0;
		for (int j = 100; j >= 0; j--) {
			if (v1[j] != 0) {
				dig = j; break;
			}
		}
		if (dig >= 80) cout << "overflow" << endl;
		else {
			for (int j = dig; j >= 0; j--) {
				cout << v1[j];
			}
			cout << endl;
		}
	}
}