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 <cmath>
#include <cstdlib>
#include <cstring>

using namespace std;

const int MAX_INPUT = 1000000;
const int ARRAY_SIZE = 11;
const int MAX_LEN = 8;
char inputA[MAX_INPUT];
char inputB[MAX_INPUT];

void toBigInt(char *str, long *r) {
    int len = strlen(str);
    int endIndex = ARRAY_SIZE - (len / MAX_LEN) - 1;

    {
        int offset = 0;
        for (int i = 0; i < ARRAY_SIZE; ++i) {
            char temp[MAX_LEN + 1] = { 0 };
            int readLen = ((len - offset) < MAX_LEN) ? len - offset : MAX_LEN;
            char* start = str + len - offset - readLen;

            strncpy(temp, start, readLen);
            r[ARRAY_SIZE - i- 1] = (long)atoi(temp);
            offset += readLen;
        }
    }
}

int main() {
    const char OVER[] = "overflow\n";
    int n = 0;
    scanf("%d", &n);

    for (int i = 0; i < n; ++i) {
        scanf("%s\n%s", &inputA, &inputB);
        long a[ARRAY_SIZE] = { 0 };
        long b[ARRAY_SIZE] = { 0 };
        long r[12] = { 0 };
        int lenA = 0;
        int lenB = 0;
        const int MAX_INPUT_LEN = 80;
        lenA = strlen(&inputA[0]);
        lenB = strlen(&inputB[0]);
        if ((MAX_INPUT_LEN < lenA) || (MAX_INPUT_LEN < lenB)) {
            printf(OVER);
            continue;
        }

        toBigInt(inputA, a);
        toBigInt(inputB, b);
        for (int i = 0; i < ARRAY_SIZE; ++i) {
            int curRIndex = 12 - i - 1;
            r[curRIndex] += a[ARRAY_SIZE - i - 1] + b[ARRAY_SIZE - i - 1];
            const int MAX = 99999999;
            if (MAX < r[curRIndex]) {
                r[curRIndex - 1] = r[curRIndex] / (MAX + 1);
                r[curRIndex] %= (MAX + 1);
            }
        }

        if (9999999 < r[2]) {
            printf(OVER);
            continue;
        }

        {
            bool started = false;
            bool noOutput = true;
            for (int i = 0; i < 12; ++i) {
                if (!started && (0 < r[i])) {
                    started = true;
                    printf("%d", r[i]);
                    noOutput = false;
                    continue;
                }

                if (started) {
                    long temp = (r[i] == 0) ? 1 : r[i];
                    for (int j = 0; temp * pow(10, j) < 10000000; ++j) {
                        printf("0");
                    }

                    printf("%d", r[i]);
                }
            }

            if (noOutput) {
                printf("0");
            }
        }
        printf("\n");

        for (int i = 0; i < MAX_INPUT; ++i) {
            inputA[i] = 0;
            inputB[i] = 0;
        }
    }

    return 0;
}

C++: //include
//------------------------------------------
#include <bits/stdc++.h>

using namespace std;

////typedef
////------------------------------------------
//typedef vector<int> vi;
//typedef vector<vi> vii;
//typedef vector<string> vs;
//typedef vector<bool> vb;
//typedef vector<vb> vbb;
//typedef pair<int, int> pii;
//typedef long long ll;
//typedef unsigned long long ull;
//
////container util
////------------------------------------------
//#define all(a)  (a).begin(),(a).end()
//#define rall(a) (a).rbegin(), (a).rend()
//#define pb push_back
//#define mp make_pair
//#define iter(i,c) for(auto i=(c).begin(); i!=(c).end(); ++i)
//
////repetition
////------------------------------------------
//#define loop(i,a,b) for(int i=(a);i<(b);++i)
//#define rep(i,n)  loop(i,0,n)
//
////constant
////--------------------------------------------
//const double eps = 1e-10;
//const double pi  = acos(-1.0);
//const double inf = (int)1e8;
//
//// output vector
//// ------------------------------------------
//namespace std {
//    template<typename T> ostream & operator<<(ostream& os, vector<T> const& v){
//        for(auto it=v.begin(); it!=v.end(); ++it){
//            os << *it << (it+1==v.end() ? "" : ",");
//        }
//        return os;
//    }
//}
//
////clear memory
//#define clr(a) memset((a), 0 ,sizeof(a))

string IntToString(int number) {
    stringstream ss;
    ss << number;
    return ss.str();
}

int main(){
    int n;
    cin >> n;
    for(int p=0; p < n; p++){
        string ans;
        string s, t;
        cin >> s >> t;
        if(s.size() > t.size()) swap(s, t);


        int q = t.size()-s.size();
        for(int i=0; i < q; i++) s = "0" + s;

        int up = 0;
        for(int i=s.size()-1; 0 <= i; i--){
            int d = atoi(s.substr(i, 1).c_str());
            int f = atoi(t.substr(i, 1).c_str());
            ans = IntToString((d+f+up)%10) + ans;

            if(0 <= d+f+up-10) up = 1;
            else up = 0;
        }
        if(up == 1) ans = IntToString(1) + ans;
        cout << ans << endl;
     }
}