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 <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_n(a,80,0); fill_n(b,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=="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=="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;}
		}
		int d=0;
		for(int j=0; j<80; j++){
			c[j] = (a[j]+b[j]+d)%10;
			d = (a[j]+b[j]+d)/10;
		}
		bool 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 <iostream>
#include <cmath>

using namespace std;

int main(){
	int N; cin >> N;
	for(int i = 0; i < N; i++){
		long double a, b;
		cin >> a >> b;
		if(log10(a) >= 80 || log10(b) >= 80){
			cout << "overflow" << endl; 
		}else{
			cout << a + b << endl;
		}
	}
	return 0;
}

C++: #include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
typedef vector <int> VI;

VI string_to_vi( string number )
{
	VI converted( number.size() );
	for ( int i = 0; i < number.size(); i++ ) converted[i] = (int)( number[i] - '0' );
	return converted;
}

VI add( VI left, VI right )
{
	VI result;
	reverse( left.begin(), left.end() );
	reverse( right.begin(), right.end() );
	VI::iterator it_left = left.begin();
	VI::iterator it_right = right.begin();

	int carry = 0;
	while ( it_left != left.end() || it_right != right.end() )
	{
		int l = 0, r = 0;
		if ( it_left != left.end() ) l = *it_left;
		if ( it_right != right.end() ) r = *it_right;

		result.push_back( ( l + r + carry ) % 10 );
		carry = ( l + r + carry >= 10 ) ? 1 : 0;

		if ( it_left != left.end() ) it_left ++;
		if ( it_right != right.end() ) it_right ++;
	}
	if ( carry ) result.push_back( 1 );

	reverse( result.begin(), result.end() );
	return result;
}

int main( void )
{
	int n; cin >> n;
	for ( int i = 0; i < n; i++ )
	{
		string input_a, input_b;
		cin >> input_a >> input_b;

		VI a = string_to_vi( input_a );
		VI b = string_to_vi( input_b );
		VI c = add( a, b );

		for ( VI::iterator it = c.begin(); it != c.end(); it++ ) cout << *it;
		cout << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <set>
#include <queue>
#include <stack>
#include <string>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
 
#define rep(i, n) for(int i = 0; i < n; i ++)
#define ALL(T) T.begin(), T.end()
#define mp make_pair
#define pb push_back
#define MEMSET(v, h) memset((v), h, sizeof(v))
 
using namespace std; 

typedef pair<int, int> pii;
typedef long long ll;
typedef vector<int> vi;
typedef vector<string> vs;

const int INF = 1 << 24;
 
int main(void){
    int n; cin >> n;

    while(n --){
        vi res(81); fill(ALL(res), 0);

        rep(i, 2){
            string in; cin >> in;
            rep(j, in.size() + 1){
                if(j != in.size()) res[j] += in[in.size() - j - 1] - '0';
                for(int l = 0; res[j + l] > 9; l ++) res[j + l + 1] ++, res[j + l] %= 10;
            }
        }

        if(res[80]){ cout << "overflow" << endl; continue; }

        bool ok = false;
        for(int i = 79; i >= 0; i --){
            if(!ok) if(res[i]) ok = true;
            if(ok) cout << res[i];
        }
        cout << endl;
    }
 
    return 0;
}

C++: (n=gets.to_i).times{puts((a=gets.to_i+gets.to_i)>=10**80?"overfllow":a)}