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<cstring>

#define MAX 80

int main(){
	int i, j, n, na, nb, flg;
//	long a[10], b[10];
	char a[MAX*10]={'\0'}, b[MAX*10]={'\0'}, tp;

	scanf("%d", &n);
	while(n--){

	scanf("%s", a);
	na=strlen(a);
	for(i=0, j=na; i<na/2; i++, j--){
		tp=a[i]; a[i]=a[j-1]; a[j-1]=tp;
	}
	scanf("%s", b);
	nb=strlen(b);
	for(i=0, j=nb; i<nb/2; i++, j--){
		tp=b[i]; b[i]=b[j-1]; b[j-1]=tp;
	}


	if(na>nb){
 		for(i=0, flg=0; i<nb; i++){
			flg+=a[i]-'0'+b[i]-'0';
			a[i]=flg%10+'0';
			flg/=10;
	}	
		for(i=nb; i<na; i++){
			flg+=a[i]-'0';
			a[i]=flg%10+'0';
			flg/=10;
	}
		if(flg) a[i]='1';
	}
	else {
		for(i=0, flg=0; i<na; i++){
			flg+=a[i]-'0'+b[i]-'0';
			a[i]=flg%10+'0';
			flg/=10;
	}			
		for(i=na; i<nb; i++){
			flg+=b[i]-'0';
			a[i]=flg%10+'0';
			flg/=10;
	}
		if(flg) a[i]='1';
	}


	j=strlen(a);

	if((na>MAX) || (nb>MAX)||(j>MAX))
		printf("overflow\n");
	else{
		for(i=j; i>0; i--) printf("%c",a[i-1]);
		printf("\n");
	}
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <deque>
#include <list>
#include <string>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <algorithm>

using namespace std;

int N;
int size[2];
string num[3];

int main() {
	cin >> N;

	for (int i = 0; i < N; i++) {
		cin >> num[0];
		cin >> num[1];

		size[0] = num[0].size();
		size[1] = num[1].size();
		if (size[0] > 80 || size[1] > 80) cout << "overflow" << endl;
		else {
			int sum = 0;
			bool kuriage = false;
			bool overflow = false;
			num[2] = "";
			for (int j = 0; j < 81; j++) {
				if (j == 80 && kuriage) {
					overflow = true;
					break;
				}
				if (j >= size[0] && j >= size[1] && !kuriage) break;
				
				if (kuriage) sum = 1;
				else sum = 0;
				
				if (j < size[0]) {
					sum += num[0][size[0] - j - 1] - '0';
				}
				if (j < size[1]) {
					sum += num[1][size[1] - j - 1] - '0';
				}
				
				if (sum >= 10) {
					sum -= 10;
					kuriage = true;
				} else kuriage = false;

				num[2] = (char)('0' + sum) + num[2];
			}
			if (overflow) cout << "overflow" << endl;
			else cout << num[2] << endl;
		}
	}

	return 0;
}

/*@@@@@@@@@@@@@@@@@@@@@@@@@*/
/*@                       @*/
/*@ debug output erased ? @*/
/*@                       @*/
/*@@@@@@@@@@@@@@@@@@@@@@@@@*/

C++: #include <cstdio>
using namespace std;

int main(){
	int N;
	char str1[90], str2[90];
	int num1[80], num2[80], sum[80];
	int pos, pos2, up;
	
	scanf("%d", &N);
	for(int n = 0; n < N; n++){
		for(int i = 0; i < 90; i++){
			str1[i] = 0;
			str2[i] = 0;
		}
		for(int i = 0; i < 80; i++){
			num1[i] = 0;
			num2[i] = 0;
			sum[i] = 0;
		}
		scanf("%s", str1);
		scanf("%s", str2);
		
		pos = 89;
		while(str1[pos] == 0 && pos >= 0) pos--;
		pos2 = 0;
		while(str1[pos] != 0 && pos >= 0){
			num1[pos2++] = str1[pos--] - 48;
		}
		pos = 89;
		while(str2[pos] == 0 && pos >= 0) pos--;
		pos2 = 0;
		while(str2[pos] != 0 && pos >= 0){
			num2[pos2++] = str2[pos--] - 48;
		}
		
		/*for(int i = 0; i < 80; i++) printf("%d", num1[i]);
		printf("\n");
		for(int i = 0; i < 80; i++) printf("%d", num2[i]);
		printf("\n");*/
		
		up = 0;
		for(int i = 0; i < 80; i++){
			sum[i] = num1[i] + num2[i] + up;
			up = sum[i] / 10;
			sum[i] = sum[i] % 10;
		}
		
		if(up > 0 || sum[79] > 0) printf("overflow\n");
		else{
			pos = 79;
			while(sum[pos] == 0 && pos >= 0) pos--;
			if(pos < 0) printf("0");
			while(pos >= 0){
				printf("%d", sum[pos--]);
			}
			printf("\n");
		}
	}
	
	return 0;
}

C++: #include<iostream>
#include<string>
using namespace std;
int main(){
int n,i,j,k,l,m,u,v,c;
string s,t,w;
cin>>n;
for(k=0;k<n;k++){
cin>>s>>t;
l=s.size();if(l>80){cout<<"overflow"<<endl;continue;}
m=t.size();if(m>80){cout<<"overflow"<<endl;continue;}
if(l<m){w=s;s=t;t=w;}
for(c=0,i=l-1,j=m-1;j>=0;i--,j--){
u=s[i]-48;v=t[j]-48;
u+=(v+c);
if(c=(u>9))u-=10;
s[i]=u+48;
}
for(;i>=0;i--){
u=s[i]-48;
u+=c;
if(c=(u>9))u-=10;
s[i]=u+48;
}
if(l==80&&c==1){cout<<"overflow"<<endl;continue;}
if(c==1)cout<<"1";cout<<s<<endl;
}
return 0;
}