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<algorithm>
#include<string>


#define MAX 1000


//99999999999999999999999999999999999999999999999999999999999999999999999999999999

using namespace std;


int main()
{
	int n = 0;
	string in[2];
	char out[MAX] = {NULL};

	cin >> n;

	for (int i = 0; i < n; i++){

		in[0].resize(0);
		in[1].resize(0);

		cin >> in[0] >> in[1];

		for (int i = 0; i < MAX; i++){
			out[i] = '\0';
		}

		int count = in[0].size() - 1;

		for (int i = 0; i < in[0].size(); i++){
			out[count--] += in[0][i];
		}

		count = in[0].size();
		int count2 = in[1].size() - 1;

		count = max(count , count2) - 1;

		for (int i = 0; i < in[1].size(); i++){
			if (out[i] != '\0'){
				out[i] -= '0';
			}
			out[i] += in[1][count2--];
			count--;
		}
		
		int i = 0;
		for (i = 0; out[i] != '\0'; i++){
			;
		}

		bool flag = false;


		for (int j = 0; j < i; j++){
			if (out[j] > '9'){
				out[j] -= 10;
				out[j + 1] += 1;
			}
		}

		if (out[i] > '\0' && out[i] < '0'){
			out[i] += '0';
		}
		
		for (i = 0; i < out[i] != '\0'; i++){
			;
		}

		for (int j = 0; j < i / 2; j++){
			char tmp = out[j];
			out[j] = out[i - j - 1];
			out[i - j - 1] = tmp;
		}

		for (i = 0; out[i]; i++){

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

using namespace std;

int main (void) {
    int N;
    cin >> N;
    while (N--) {
        string s1, s2;
        cin >> s1;
        cin >> s2;
        vector<int> n1, n2, res;
        for (int i = s1.size(); i--;) {
            n1.push_back((int)(s1[i] - '0'));
        }
        for (int i = s2.size(); i--;) {
            n2.push_back((int)(s2[i] - '0'));
        }
        if (n1.size() < n2.size()) {
            for (int i = n1.size(); i < n2.size(); i++) {
                n1.push_back(0);
            }
        } else if (n2.size() < n1.size()) {
            for (int i = n2.size(); i < n1.size(); i++) {
                n2.push_back(0);
            }
        }
        int s, c = 0;
        for (int i = 0; i < n1.size(); i++) {
            s = n1[i] + n2[i] + c;
            res.push_back(s % 10);
            c = s / 10;
        }
        if (c != 0) {
            res.push_back(c);
        }
        if (res.size() > 80) {
            cout << "overflow" << endl;
        } else {
            int i = res.size();
            while (i > 0 && res[i - 1] == 0) {
                i--;
            }
            while (i--) {
                cout << res[i];
            }
            cout << endl;
        }
    }
    return 0;
}

C++: #include <iostream>
#include <string>
#include <algorithm>

using namespace std;

int main(){
  string str1,str2;
  int testnum;

  cin>>testnum;
  int t=0;
  while(t<testnum&&cin>>str1>>str2){
    string sumstr;
    reverse(str1.begin(),str1.end());
    reverse(str2.begin(),str2.end());

    unsigned size=min(str1.size(),str2.size());
    unsigned i;
    unsigned carry=0;
    for(i=0;i<size;++i){
      unsigned sum=str1[i]+str2[i]+carry-'0'*2;
      sumstr.push_back(sum%10+'0');
      carry=sum/10;
    }

    string large=(str1.size()>str2.size())?str1:str2;
    for(;i<large.size();++i){
      unsigned sum=large[i]+carry-'0';
      sumstr.push_back(sum%10+'0');
      carry=sum/10;
    }

    if(carry) sumstr.push_back(carry+'0');
    reverse(sumstr.begin(),sumstr.end());
    
    if(sumstr.size()<=80)
      cout<<sumstr<<endl;
    else
      cout<<"overflow"<<endl;
    t++;
  }
}

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

//const static double	de_PI	= 3.14159265358979323846;
//const static int	de_MOD	= 1000000007;
//const static int	de_MAX	= 999999999;
//const static int	de_MIN = -999999999;

inline std::string Add_MultiplePrecision(const std::string A, const std::string B) {

	int a[200] = {0};
	int b[200] = {0};
	int c[300] = {0};

	for (unsigned int i = 0; i < A.length(); i++) {
		a[i] = A[A.length() - 1 - i] - '0';
	}
	for (unsigned int i = 0; i < B.length(); i++) {
		b[i] = B[B.length() - 1 - i] - '0';
	}

	int carry = 0;
	for (unsigned int i = 0; i < std::max(A.length(), B.length()); i++) {
		c[i] = (a[i] + b[i] + carry) % 10;
		c[i + 1] = carry = (a[i] + b[i] + carry) / 10;
	}

	int st = 299;
	while (c[st] == 0) {
		st--;
	}

	std::string ans;
	for (int i = st; i >= 0; i--) {
		ans += std::to_string(c[i]);
	}

	if (ans == "") {
		ans = "0";
	}

	return ans;
}

int main(void) {

	//std::ifstream in("123.txt");	std::cin.rdbuf(in.rdbuf());

	int n = 0;
	std::cin >> n;
	std::vector<std::string> ans;

	std::string temp1, temp2, temp3;
	while (std::cin >> temp1) {
		std::cin >> temp2;
		temp3 = Add_MultiplePrecision(temp1, temp2);
		if (temp3.length() >= 80) {
			ans.push_back("overflow");
		}
		else {
			ans.push_back(temp3);
		}
	}

	for (unsigned int i = 0; i < ans.size(); i++) {
		std::cout << ans[i] << std::endl;
	}
}