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 <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void) {

  int n;

  char buf[1000];
  char outbuf[1000];

  char c;

  int a[1000],b[1000];
  int result[1000];
  
  int sum,carry;
  int idx1,idx2;
  int maxlen;

  int i,j;

  scanf("%d",&n);

  c=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;

    if(maxlen>80) {

      printf("overflow\n");

      continue;

    }

    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 {

	outbuf[0]='1';

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

	  outbuf[j+1]=result[maxlen-j-1]+48;

	}

	outbuf[maxlen+1]='\0';

	printf("%s",outbuf);

	puts("");

      }

    }

    else {

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

	outbuf[j]=result[maxlen-j-1]+48;

      }

      outbuf[maxlen]='\0';

      printf("%s",outbuf);

      puts("");

    }

  }

  return 0;

}

C++: #include<iostream>
#include<string>
using namespace std;
ios::sync_with_stdio(false);

int main(){
    int n;
    for(cin>>n;n--;){
        int k=0;
        string a,b;
        cin >> a;
        cin >> b;
        if(a.size() < b.size()) swap(a,b);//????????????a>b?????????
        while(b.size() < a.size()) b = '0' + b;//????????????a==b?????????
        for(int i=a.size()-1;i>=0;i--){//???????????????????????????
            a[i] += b[i] - '0' + k;
            if(a[i] > '9'){
                a[i]-=10;
                k = 1;
            }
            else k = 0;
        }
        if(k)   a="1"+a;//??°??????????????????????????????????¶?????????¨???
        if(a.size() > 80)   cout << "overflow" << "\n";
        else    cout << a << "\n";
    }
    return 0;
}

C++: #include<iostream>
#include<string>
#include<algorithm>
#define N 1000
using namespace std;
int main(){
  
  int n,anum,bnum;
  cin >> n;
  for(int i = 0;i < n;i++){
    string a,b,c,tmp;
    cin >> a >> b;
      if(a.size() < b.size()){swap(a,b);}
      for(int k = 0;k< a.size();k++)
	c[k] = '0';
      for(int k = 0;k < b.size();k++){
	c[k] = b[b.size()-1-k];
      }
      for(int k = 0;k < a.size();k++)
	   {b[k] = c[k]; c[k] = a[k];}
      for(int k = 0;k < a.size();k++){
      	a[a.size()-k-1] = c[k];
	  tmp[k] = '0';}

      //for(int k = 0;k <= a.size();k++)
      //	cout << a[k] ;
      //cout << endl;
      //for(int k = 0;k <= a.size();k++)
      //	cout << b[k] ;
      //cout << endl;
      
        for(int k = 0;k < a.size();k++){
	  //  cout << a[k] << b[k] << " " <<tmp[k] << endl;
	c[k] = a[k] + b[k] + tmp[k] -'0' -'0';
	
	if(c[k] > '9'){ tmp[k+1] = '1'; c[k] = c[k] - ':' + '0'; }
	}

	if(a.size() < 80 && tmp[a.size()] == '1'){ cout << tmp[a.size()];
      for(int k = a.size()-1;k >=0;k--){
	cout << c[k];  //cout << tmp[0];
	}

      cout << endl;
	} else {cout <<"overflow"<<endl; }
  }
}

C++: #include<cstdio>
#include<cmath>
using namespace std;

int main(){
	int n,t,i;
	char a[100],b[100],x[100],y[100];
	scanf("%d",&n);
	for(int o=0;o<n;o++){
		t=0;
		scanf("%s %s",a,b);
		for(i=0;a[i]!='\0';i++){}
		for(int j=0;j<i;j++){
			x[j]=a[i-j-1];
		}
		for(;i<100;i++){
			x[i]='0';
		}
		for(i=0;b[i]!='\0';i++){}
		for(int j=0;j<i;j++){
			y[j]=b[i-j-1];
		}
		for(;i<100;i++){
			y[i]='0';
		}
		for(i=0;i<99;i++){
			x[i]+=y[i]-'0';
			if(x[i]>'9'){
				x[i]-=10;
				x[i+1]+=1;
			}
		}
		for(i=99;i>=0;i--){
			if(x[i]!='0' || t){
				if(i>78){
					printf("overflow");
					break;
				}
				printf("%c",x[i]);
				t=1;
			}
		}
		printf("\n");
	}
	return 0;
}

C++: // 2012/10/28 Tazoe

#include <iostream>
#include <string>
using namespace std;

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

	for(int i=0; i<N; i++){
		string S1, S2;
		cin >> S1;
		cin >> S2;

		if(S1.size()<S2.size()){
			string tmp = S1;
			S1 = S2;
			S2 = tmp;
		}

		if(S1.size()>80){
			cout << "overflow" << endl;
			continue;
		}

		int A[80];
		int C = 0;
		for(int j=0; j<S1.size(); j++){
			int tmp = (int)(S1[S1.size()-1-j]-'0')+C;
			if(j<S2.size()){
				tmp += (int)(S2[S2.size()-1-j]-'0');
			}

			A[j] = tmp%10;
			C = tmp/10;
		}

		if(S1.size()==80&&C==1){
			cout << "overflow" << endl;
		}
		else{
			if(C==1){
				cout << C;
			}
			for(int j=S1.size()-1; j>=0; j--){
				cout << A[j];
			}
			cout << endl;
		}
	}

	return 0;
}