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] = -1;
    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] == -1 && r.d[i] == -1){
	if(!updigit)
	  continue;
	this->d[i] = updigit+'0';
	updigit = 0;
	tmp++;
      }else{
	if(this->d[i] != -1)
	  a = toI(this->d[i]);
	if(r.d[i] != -1)
	  b = toI(r.d[i]);
	int n = a + b + updigit;
	updigit = n / 10;
	this->d[i] = (n % 10)+'0';
      }
    }
    this->size = tmp;
    return;
  }

  void print()
  {
    puts("overflow");
    /*    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);
  while(d--){
    char s1[128], s2[128];
    scanf("%s",s1);
    scanf("%s",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 <cstdio>
#include <cstdlib>
#include <cmath>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <sstream>
#include <queue>
#include <cstring>
#include <functional>

using namespace std;

#define REP(i,a,b) for((i)=(a);(i)<(int)(b);(i)++)
#define rep(i,n) REP(i,0,n)
// BEGIN CUT HERE
#define foreach(c,itr) for(typeof((c).begin()) itr=(c).begin();itr!=(c).end();itr++)
template<class T> inline string toString(T x){ostringstream sout;sout<<x;return sout.str();}
// END CUT HERE

int main(){
  int i, j, n;
  char tmp;

  scanf("%d",&n);
  rep(i,n){
    string str1, str2, res;
    cin >> str1;
    cin >> str2;

    vector<int> a(82, 0), b(82, 0);

    rep(j,81){
      int sum = a[j] + b[j];
      if(sum >= 10){ sum %= 10; a[j+1]++;}
      res += (sum + '0');
    }

    reverse(res.begin(), res.end());
    int f = 0;
    rep(j,res.length()){
      if(res[j] != '0') f = 1;
      if(f) cout << res[j];
    }

    cout << endl;
  }

  return 0;
}

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

int main(){
	int n;
	cin >> n;
	for(int rep=0; rep<n; rep++){
		string str[3];
		cin >> str[0] >> str[1];
		int ml = max(str[0].length(), str[1].length())+1;
		for(int i=0; i<2; i++){
			reverse(str[i].begin(), str[i].end());
			int len = str[i].length();
			for(int j=0; j<ml-len; j++){
				str[i] += "0";
			}
		}
		str[2] = "";
		int c=0;
		for(int i=0; i<ml; i++){
			int n = (str[0][i]-'0')+(str[1][i]-'0')+c;
			if(n>9) c=1;
			else c=0;
			str[2] += n%10 +'0';
		}
		if(str[2].back()=='0') str[2].pop_back();
		reverse(str[2].begin(), str[2].end());
		if(str[2].length() > 80){
			cout << "overflow" << endl;
		}else{
			cout << str[2] << endl;
		}
	}
	return 0;
}

C++: #include <stdio.h>

int main(void) {

  int n;

  char buf[100];

  int a[100],b[100];
  int result[100];
  
  int sum,carry;
  int idx1,idx2;
  int maxlen;

  int i,j;

  scanf("%d",&n);

  getchar();

  for(i=0;i<n;i++) {

    fgets(buf,sizeof(buf),stdin);

    idx1=0;

    while(buf[idx1]!='\n') {

      a[idx1]=buf[idx1]-48;

      idx1++;

    }

    //for(j=0;j<idx1;j++) printf("%d",a[j]);

    fgets(buf,sizeof(buf),stdin);

    idx2=0;

    while(buf[idx2]!='\n') {

      b[idx2]=buf[idx2]-48;

      idx2++;

    }

    if(idx1>idx2) maxlen=idx1;
    
    else maxlen=idx2;

    carry=0;

    for(j=0;j<maxlen;j++) {

      if(j<idx1 && j<idx2) sum=a[idx1-j-1]+b[idx2-j-1]+carry;

      else if(j>=idx1) sum=b[idx2-j-1]+carry;

      else sum=a[idx1-j-1]+carry;


      if(sum>=10) carry=1;

      else carry=0;

      result[j]=sum%10;

    }
    //printf("%d\n",carry);
    if(carry==1) {

      if(maxlen>=80) printf("overflow\n");

      else {

	printf("1");

	for(j=maxlen-1;j>=0;j--) {

	  printf("%d",result[j]);

	}

	putchar('\0');

	puts("");

      }

    }

    else {

      for(j=maxlen-1;j>=0;j--) {

	printf("%d",result[j]);

      }

      puts("");

    }

  }

  return 0;

}