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<stdio.h>
#include<string.h>

int main()
{
	char  input1[1001]={0},input2[1001]={0};
	int   output[1002]={0};
	int lengs1=0,lengs2=0,lengs3=0,lengs4=0,count;	
	
	scanf("%d",&count);

	for(int c=0;c<count;c++)
	{
		int i,j=1,k;
		scanf("%s",&input1);
		scanf("%s",&input2);
		if(strlen(input1)>80 || strlen(input2)>80)
		{
			printf("overflow\n");
			continue;
		}
		lengs1=strlen(input1);
		lengs2=strlen(input2);
		lengs3=(lengs1>=lengs2)?lengs1+1:lengs2+1;
		lengs4=lengs3;
		while(lengs3>=0 && lengs1>=0 && lengs2>=0)
		{
			output[lengs3]+=(input1[lengs1--]-'0')+(input2[lengs2--]-'0');
			if(output[lengs3]>=10)
			{
				output[lengs3]%=10;
				output[lengs3-1]+=1;
			}
			lengs3--;
		}

		if(lengs1>=0||lengs2>=0)
		{
			while(lengs1>=0)
			{
				output[lengs3]+=(input1[lengs1--]-'0');
				if(output[lengs3]>=10)
				{
					output[lengs3]%=10;
					output[lengs3-1]+=1;
				}
				lengs3--;
			}
			while(lengs2>=0)
			{
				output[lengs3]+=(input2[lengs2--]-'0');
				if(output[lengs3]>=10)
				{
					output[lengs3]%=10;
					output[lengs3-1]+=1;
				}
				lengs3--;
			}
		}
		if(lengs4>80)
		{
			printf("overflow\n");
			continue;
		}
		if(output[0]!=0)
			j=0;
		for(i=j;i<lengs4;i++)
		{
			printf("%d",output[i]);
		}
		printf("\n");
		for(k=0;k<1000;k++)
		{
			input1[k]=0;
			input2[k]=0;
			output[k]=0;
		}
	}
}

C++: #include <iostream>
#include <algorithm>
using namespace std;
int main(){
  string num1,num2,tmp;
  int n;

  cin >> n;
  while(n--){

    cin >> num1 >> num2;

    if((int)num1.size() < (int)num2.size()){
      tmp = num2;
      num2 = num1;
      num1 = tmp;
    }

    if(num1.size() > 80){
      cout << "overflow" << endl;
      continue;
    }

    for(int i = 0 ; i < (int)num1.size() ; i++ )tmp[i] = num1[i];

    for(int i = (int)num1.size() - 1 ; i >= 0 ; i-- )
      {
	num1[i] = tmp[(int)num1.size() - 1 - i];
      }
    for(int i = 0 ; i < (int)num2.size() ; i++ )tmp[i] = num2[i];

    for(int i = (int)num2.size() - 1  ; i >= 0 ; i-- )
      {
	num2[i] = tmp[(int)num2.size() - 1 - i];
      }

    for(int i = (int)num2.size() ; i < (int)num1.size() ; i++ )num2+='0';

    char tmp2 = '0';
    string ans;

    for(int i = 0 ; i < num1.size() ; i++ ){
      if((tmp2 - '0') + (num1[i] - '0') + (num2[i] - '0') > 9){
	ans += (char)(((tmp2 - '0') + (num1[i] - '0') + (num2[i] - '0') - 10) + '0');
	tmp2 = '1';
      } else {
	ans += (char)(((tmp2 - '0') + (num1[i] - '0') + (num2[i] - '0')) + '0');
	tmp2 = '0'; 
      }
    }
  
    if((int)((tmp2 - '0') + (num1[num1.size() - 1] - '0') + (num2[num1.size() - 1] - '0')) > 9)ans+='1'; 
    if(ans.size() > 80){
      cout << "overflow" << endl;

    }else{

      for(int i = (int)ans.size() ; i >= 0 ; i-- ){
	cout << ans[i];
      }  
      cout << endl;
    }
  }

  return 0;
}

C++: #include<iostream>
#include<string>
#include<algorithm>
using namespace std;
int main(){
	int n;
	cin >> n;
	for(int i = 1; i <= n; i++){
		string a, b;
		cin >> a >> b;
		if(a.size() < b.size()) swap(a, b);
		reverse(a.begin(), a.end());
		reverse(b.begin(), b.end());
		string ans;
		bool carryover = false;
		for(int j = 0; j < b.size(); j++){
			int num;
			if(carryover) num = (a[j] - '0') + (b[j] - '0') + 1;
			else num = (a[j] - '0') + (b[j] - '0');
			if(num >= 10) carryover = true;
			else carryover = false;
			ans.push_back(num % 10 + '0');
		}
		for(int j = b.size(); j < a.size(); j++){
			int num;
			if(carryover) num = (a[j] - '0') + 1;
			else num = (a[j] - '0');
			if(num >= 10) carryover = true;
			else carryover = false;
			ans.push_back(num % 10 + '0');
		}
		if(carryover) ans.push_back('1');
		reverse(ans.begin(), ans.end());
		if(ans.size() > 80) cout << "overflow" << endl;
		else cout << ans << endl;
	}
	return 0;
}