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 <algorithm>
#include <cmath>
#include <climits>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <cassert>
#include <functional>

using namespace std;

#define LOG(...) printf(__VA_ARGS__)
//#define LOG(...)
#define FOR(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define RSORT(c) sort((c).rbegin(),(c).rend())
#define CLR(a) memset((a), 0 ,lengthof(a))

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int dx[] = { -1, 0, 1, 0 }; const int dy[] = { 0, 1, 0, -1 };

int main() {
	int n;
	cin >> n;
	while (n--){
		string s1, s2;
		cin >> s1 >> s2;
		string ans = "";
		int s1l = s1.length();
		int s2l = s2.length();
		bool up = false;
		REP(i, max(s1l, s2l)){
			int a = up ? 1 : 0;
			if (s1l - i - 1 >= 0)
				a += s1.c_str()[s1l - i - 1] - '0';
			if (s2l - i - 1 >= 0)
				a += s2.c_str()[s2l - i - 1] - '0';
			up = (a >= 10);
			ans = to_string(a % 10) + ans;
			if (max(s1l, s2l) - i-1 == 0 && up)ans = "1" + ans;
		}
		if (ans.length()<=80)
		cout<<ans<<endl;
		else
			cout << "overflow"<<endl;
	}
}

C++: #include<bits/stdc++.h>
using namespace std;
char str[102],str1[102],ans[102];
int sam(int ma1,int ma2)
{
    int co,carry=0,a,b;
    for(int i=0;ma1-i>=0||ma2-i>=0||carry==1;i++){
            if(ma1-i>=0&&ma2-i>=0){
                    a=str[ma1-i]-'0';
                    b=str1[ma2-i]-'0';
                    if(a+b+carry>=10){
                        ans[i]=a+b+carry-10+'0';
                        carry=1;
                    }
                    else {
                        ans[i]=a+b+carry+'0';
                        carry=0;
                    }
            }
            else if(ma1-i>=0){
                    a=str[ma1-i]-'0';
                    if(a+carry>=10){
                        ans[i]=a+carry-10+'0';
                        carry=1;
                    }
                    else {
                        ans[i]=a+carry+'0';
                        carry=0;
                    }
            }
            else if(ma2-i>=0){
                    b=str1[ma2-i]-'0';
                    if(a+carry>=10){
                        ans[i]=a+carry-10+'0';
                        carry=1;
                    }
                    else {
                        ans[i]=a+carry+'0';
                        carry=0;
                    }
            }
            else {
                ans[i]='0'+1;
                return i;
            }
        co=i;

    }
    return co;

}
int main()
{
    int a,b,n;
    cin>>n;
    for(int i=0;i<n;i++){
        cin>>str>>str1;
        a=strlen(str);
        b=strlen(str1);
        a=sam(a,b);
        for(int j=a;j>0;j--)cout<<ans[j];
        cout<<endl;
    }

}

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

int main(){
  int n;
  string a,b;
  cin>>n;
  while(cin>>a>>b){
    int asize=a.length();
    int bsize=b.length();
    int smax=max(asize,bsize);
    bool flag=false;
    int s;
    stringstream ss;
    for(int i=0;i<smax;i++){
      if(asize-i-1<0) s=strtol(b.substr(bsize-i-1,1).c_str(),NULL,0);
      else if(bsize-i-1<0) s=strtol(a.substr(asize-i-1,1).c_str(),NULL,0);
      else s=strtol(a.substr(asize-i-1,1).c_str(),NULL,0)+strtol(b.substr(bsize-i-1,1).c_str(),NULL,0);
      if(flag) s++;
      ss<<s%10;
      if(s>9)
	flag=true;
      else
	flag=false;
    }
    if(flag) cout<<1;
    string ans=ss.str();
    for(string::reverse_iterator rit=ans.rbegin();rit!=ans.rend();rit++)
    cout<<*rit;
    cout<<endl;
  }
  return 0;
}