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>

#define DEGITS 80

void load(int a[]);
void print(int a[]);

int main(void){
    int a[DEGITS]; // a[0] = LSD
    int b[DEGITS];
    int n;
    int cry;
    
    scanf("%d", &n);
    for (int i=0; i<n; i++){
        // reset
        for (int i=0; i<DEGITS; i++){
            a[i]=b[i]=0;
        }
        // load
        load(a);
        load(b);
        // add ( a <- a + b )
        cry=0;
        for (int d=0; d<DEGITS; d++){
            a[d] += (b[d] + cry);
            cry = a[d]/10;
            if (a[d]>9){
                a[d]-=10;
            }
        }
        // print
        if (cry){
            printf("overflow\n");
        } else{
            print(a);
        }
    }

    return 0;
}

void load(int a[]){
    char *pt;
    char st[DEGITS+1];
    
    scanf("%s", st);
    for (pt=st; *pt!='\0'; pt++) ;
    for (int i=0; pt!=st; i++){
        a[i] = *(--pt)-'0';
    }
}

void print(int a[]){
    int d;
    
    for (d=DEGITS-1; d>0; d--){ 
        if (a[d] != 0) break;
    }
    for (; d>0; d--) printf("%d", a[d]);
    printf("%d\n", a[0]);
}

C++: #include <iostream>
#include <queue>
#include <stack>
#include <vector>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <string>
#include <cmath>
#include <complex>
#include <map>
using namespace std;

#define rep(i,n) for(int i=0;i<int(n);++i)
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define EPS 1e-8
#define F first
#define S second

static const double PI=6*asin(0.5);
typedef pair<double,double> P;
typedef complex<double> CP;
typedef long long ll;


int a[100],b[100],c[100];
string s;

int main(){
	int n;
	cin>>n;
	rep(i,n){
		memset(a,0,sizeof(a));
		memset(b,0,sizeof(b));
		memset(c,0,sizeof(c));
		cin>>s;
		//cout<<s<<endl;
		//cout<<s.size()<<endl;
		if(s.size()>80){
			cout<<"overflow\n";
			continue;
		}
		rep(j,s.size()){
			a[90-j]=s[s.size()-j-1]-'0';
			//cout<<s[s.size()-j-1]-'0';
		}
		//cout<<a[87]<<endl;
		cin>>s;
		if(s.size()>80){
			cout<<"overflow\n";
			continue;
		}
		rep(j,s.size()){
			b[90-j]=s[s.size()-j-1]-'0';
		}
		/*
		rep(j,91) cout<<a[j];
		cout<<endl;
		rep(j,91) cout<<b[j];
		cout<<endl;
		*/
		int t=0;
		for(int j=90;j>=0;j--){
			c[j]=(a[j]+b[j]+t)%10;
			if((a[j]+b[j]+t)>9) t=1;
			else t=0;
		}
		bool f=true;
		/*
		rep(j,91) cout<<c[j];
		cout<<endl;
		*/
		rep(j,91){
			if(f&&c[j]!=0){
				f=false;
				if(j<=10){
					cout<<"overflow";
					break;
				}
			}
			if(!f) cout<<c[j];
		}
		cout<<endl;
		
	}
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <cctype>
#include <cstdio>
#include <math.h>
#include <map>
#include <queue>
#include <string>
using namespace std;

int N,ans[81],a,b,la,lb,up,deg;
string sta,stb;

int main(){
	cin>>N;
	for(int i=0;i<N;i++){
		cin>>sta>>stb;
		la=sta.size();
		lb=stb.size();
		up=0;
		for(int i=0;i<max(la,lb)+1;i++){
			if(i>=la)a='0';
			else a=sta[la-1-i];
			if(i>=lb)b='0';
			else b=stb[lb-1-i];
			cout<<a<<" "<<b<<endl;
			if(a+b+up>105){
				ans[i]=a+b+up-10-96;
				up=1;
			}
			else{
				ans[i]=a+b+up-96;
				up=0;
			}
			if(ans[i]!=0)deg=i+1;
		}
		if(deg>80)cout<<"overflow"<<endl;
		else{
			for(int i=0;i<deg;i++)cout<<ans[deg-1-i];
			cout<<endl;
		}
	}
}

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;

  cin >> n;
  rep(i,n){
    string str1, str2, res;
    cin >> str1;
    cin >> str2;

    vector<int> a(80, 0);
    rep(j,str1.length()) a[j] = str1[str1.length()-1-j] - '0';

    vector<int> b(80, 0);
    rep(j,str2.length()) b[j] = str2[str2.length()-1-j] - '0';

    rep(j,80){
      int sum = a[j] + b[j];
      if(sum >= 10){ sum %= 10; a[j+1]++;}
      res += sum + '0';
    }

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

  return 0;
}