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 <cstdio>
#include <cstring>
#include <algorithm>

const int MAX_SIZE = 128;

#define toI(x) (x-'0')

using namespace std;

class Z
{
private:
  int size;
  char d[MAX_SIZE];
public:
  Z(char *s)
  {
    size = strlen(s);
    for(int i=0;i<MAX_SIZE - size;i++)
      d[i] = 0;
    for(int i=0,j=MAX_SIZE - size;j < MAX_SIZE; i++, j++)
      d[j] = s[i];
  }

  void add(Z r)
  {
    int tmp = max(this->size, r.size);
    int updigit = 0;
    for(int i=MAX_SIZE-1;i>=0;i--){
      int a = 0, b = 0;
      if(this->d[i] == 0&& r.d[i] == 0){
	if(!updigit)
	  goto end;
	this->d[i] = updigit+'0';
	updigit = 0;
	tmp++;
      }else{
	if(this->d[i])
	  a = toI(this->d[i]);
	if(r.d[i])
	  b = toI(r.d[i]);
	int n = a + b + updigit;
	updigit = n / 10;
	this->d[i] = (n % 10)+'0';
      }
    }
  end:
    this->size = tmp;
    return;
  }

  void print()
  {
    if(this->size > 80){
      puts("overflow");
      return;
    }
    for(int i=0;i<MAX_SIZE;i++)
      if(d[i] != -1)
	putchar(d[i]);
    puts("");
  }

  int sz()
  {
    return this->size;
  }
};

int main()
{
  int d;
  scanf("%d", &d);
  char s1[128], s2[128];  
  while(d--){
    scanf("%s%s",s1, s2);
    Z z1(s1);
    Z z2(s2);
    if(z1.sz() > 80 || z2.sz() > 80){
      puts("overflow");
      continue;
    }
    z1.add(z2);
    z1.print();
  }
  return 0;
}

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

using namespace std;

int A[95],B[95],C[95];

int main()
{
    int n;
    cin >> n;
    while(n > 0)
    {
        n--;
        string str1,str2;
        cin >> str1 >> str2;
        int len1 = str1.length();
        int len2 = str2.length();
        if(len1 < len2)
        {
            string st = str1;
            str1 = str2;
            str2 = st;
            int ll = len1;
            len1 = len2;
            len2 = ll;
        }
        for(int i = 0; i < 90; i++)
        {
            C[i] = 0;
            A[i] = 0;
            B[i] = 0;
        }

        for(int i = 0; i < len1; i++)
            A[i] = str1[len1 - 1 - i] - '0';
        for(int i = 0; i < len2; i++)
            B[i] = str2[len2 - 1 - i] - '0';
        for(int i = 0 ; i < len1; i++)
        {
            C[i] = A[i] + B[i] + C[i];
            C[i+1] = C[i] / 10;
            C[i] = C[i] % 10;
        }
        //for(int i = len2; i <len1; i++)
       // {
           //  C[i] = C[i] + A[i];
           //  C[i+1] = C[i] / 10;
          //   C[i] = C[i] % 10;
       // }


        if(C[80] > 0)
            cout << "overflow" << endl;
        else
            {
                if(C[len1] > 0)
                    len1++;
                for(int i = len1-1; i >= 0; i--)
                    cout << C[i];
                cout << endl;
            }
    }
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstring>
#include <map>
#include <queue>
#include <stack>
#include <set>
#include <functional>
#include <sstream>
using namespace std;

#define REP(i,a,n) for(int i=(a);i<(int)(n);i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define mp make_pair
#define all(x) x.begin(),x.end()

int main(){
	string in1,in2;
	int t; scanf("%d",&t);
	while(t--){
		char str[100];
		cin>>in1>>in2;
		if( in1.size()>80 || in2.size()>80 ){
			puts("overflow"); continue;
		}
		reverse(all(in1)); reverse(all(in2));
		int k = 0;
		int i;
		for(i=0; i<min(in1.size(),in2.size()); i++){
			k = (in1[i]-'0')+(in2[i]-'0') + k;
			str[i] = (k%10)+'0';
			k /= 10;
		}
		if( i==in1.size() ){ //in2
			for(; i<in2.size(); i++){
				k = (in2[i]-'0')+k;
				str[i] = (k%10)+'0';
				k /= 10;
			}
		}else{ //in1
			for(; i<in1.size(); i++){
				k = (in1[i]-'0')+k;
				str[i] = (k%10)+'0';
				k /= 10;
			}
		}
		if( k!=0 )str[i++] = k+'0';
		str[i] = 0;
		if( i>80 ){
			puts("overflow"); continue;
		}
		reverse(str,str+i);
		puts(str);
	}
	
	return 0;
}