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 <iostream>
#include <string>
#include <algorithm>

using namespace std;

char c[10] = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};

int main() {
	int n; cin >> n;
	string s1, s2;
	
	for (int i=0; i<n; i++) {
		cin >> s1 >> s2;
		reverse(s1.begin(), s1.end());
		reverse(s2.begin(), s2.end());
		
		string s = "";
		
		if (s1.size() == s2.size()) {
			int r = 0, t = 0;
			for (int i=0; i<(int)s1.size(); i++) {
				int x = s1[i]-c[0], y = s2[i]-c[0];
				int z = x + y + t;
				r = z%10;
				t = z/10;
				s += c[r];
			}
			if (t) s += c[t];
		} else if (s1.size() > s2.size()) {	
			int r = 0, t = 0;
			for (int i=0; i<(int)s2.size(); i++) {
				int x = s1[i]-c[0], y = s2[i]-c[0];
				int z = x + y + t;
				r = z%10;
				t = z/10;
				s += c[r];
			}
			if (t) {
				for (int i=(int)s2.size(); i<(int)s1.size(); i++) {
					int z = s1[i]-c[0]+t;
					r = z%10;
					t = z/10;
					s += c[r];
				}
				if (t) s += c[t];
			} else {
				for (int i=(int)s2.size(); i<(int)s1.size(); i++) s += c[s1[i]-c[0]];
			}
		} else {
			int r = 0, t = 0;
			for (int i=0; i<(int)s1.size(); i++) {
				int x = s1[i]-c[0], y = s2[i]-c[0];
				int z = x + y + t;
				r = z%10;
				t = z/10;
				s += c[r];
			}
			if (t) {
				for (int i=(int)s1.size(); i<(int)s2.size(); i++) {
					int z = s2[i]-c[0]+t;
					r = z%10;
					t = z/10;
					s += c[r];
				}
				if (t) s += c[t];
			} else {
				for (int i=(int)s1.size(); i<(int)s2.size(); i++) s += c[s2[i]-c[0]];
			}
		}
		
		reverse(s.begin(), s.end());
		cout << s << endl;
	}
	
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cstdlib>
#include <string>

using namespace std;

int main()
{
	int N; cin >> N;
	int a[80], b[80], c[80];
	string s, t, m;

	for(int i=0; i<N; i++){
		fill(a,a+80,0); fill(b,b+80,0); fill(c,c+80,0);
		cin >> s >> t;
		for(int j=s.length()-1, k=0; j>=0; j--, k++){
			m=s.substr(k,1);
			if(m=="0"){ a[j]=0;}
			else if(m=="1"){ a[j]=1;}
			else if(m=="2"){ a[j]=2;}
			else if(m=="3"){ a[j]=3;}
			else if(m=="4"){ a[j]=4;}
			else if(m=="5"){ a[j]=5;}
			else if(m=="6"){ a[j]=6;}
			else if(m=="7"){ a[j]=7;}
			else if(m=="8"){ a[j]=8;}
			else{ a[j]=9;}
		}
		for(int j=t.length()-1, k=0; j>=0; j--,k++){
			m=t.substr(k,1);
			if(m=="0"){ b[j]=0;}
			else if(m=="1"){ b[j]=1;}
			else if(m=="2"){ b[j]=2;}
			else if(m=="3"){ b[j]=3;}
			else if(m=="4"){ b[j]=4;}
			else if(m=="5"){ b[j]=5;}
			else if(m=="6"){ b[j]=6;}
			else if(m=="7"){ b[j]=7;}
			else if(m=="8"){ b[j]=8;}
			else{ b[j]=9;}
		}

		for(int j=79; j>=0; j--){
			cout << a[j];
		}
		cout << endl;
		for(int j=79; j>=0; j--){
			cout << b[j];
		}
		cout << endl;
		/*		
		int d=0;
		bool flag=false;
		for(int j=0; j<80; j++){
			c[j] = (a[j]+b[j]+d)%10;
			d = (a[j]+b[j]+d)/10;
			if(j==79 && d>0){ flag=true;}
		}
		
		if(flag){cout << "overflow";}		
		else{
				flag = false;
				for(int j=79; j>=0; j--){
					if(flag){ cout << c[j];}
					else if(c[j] != 0){ cout << c[j]; flag=true;}
				}
		}
		cout << endl;*/
	}

	return 0;
}

C++: #include <cassert>
#include <iostream>
#include <string>
#include <vector>

typedef std::vector<char> TLongInt;
TLongInt Decode(const std::string& Code)
{
    std::vector<char> Value(100, 0);
    for(int i = 0; i < Code.size(); ++i){
        Value[i] = Code[Code.size() -1 -i] - 48;
    }
    return Value;
}
TLongInt Add(const TLongInt& A, const TLongInt& B)
{
    assert(A.size() == B.size());
    TLongInt C(A.size(), 0);
    int kuriagari = 0;
    for(int i = 0; i < A.size(); ++i){
        int V = A[i] + B[i] + kuriagari;
        C[i] = V % 10;
        kuriagari = V / 10;
    }
    return C;
}

void Print(const TLongInt& Value, std::ostream& out)
{
    bool Left = true;
    for(int i = Value.size() - 1; i >= 0; --i){
        if(Value[i] == 0 && Left) continue;
        if(i >= 80){
            out << "overflow" << std::endl;
            return;
        }
        Left = false;
        out << int(Value[i]);
    }
    out << std::endl;
}

int main()
{
    int N;
    std::cin >> N;
    for(int i = 0; i < N; ++i){
        std::string first, second;
        std::cin >> first;
        std::cin >> second;
        Print(Add(Decode(first), Decode(second)), std::cout);
    }
    return 0;
}