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 <stddef.h>
#include <algorithm>
#include <iostream>
#include <iterator>
#include <string>

using namespace std;
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    string s1, s2, s3 = "";
    cin >> s1 >> s2;
    size_t m = max(s1.size(), s2.size());
    while (s1.size() < m)
      s1.insert(s1.begin(), '0');
    while (s2.size() < m)
      s2.insert(s2.begin(), '0');
    char c = 0;
    auto it1 = s1.rbegin();
    auto it2 = s2.rbegin();
    for (; it1 != s1.rend(); it1++, it2++) {
      char add = *it1 - '0' + *it2 - '0' + c;
      char ch = add % 10 + '0';
      c = add / 10;
      s3.insert(s3.begin(), ch);
    }
    if (c) s3.insert(s3.begin(), c + '0');
    cout << ((s3.size() > 80) ? "overflow" :s3) << endl;
  }
}