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<algorithm>
#include<string.h>
using namespace std;

int n;
char a[85],b[85],answer[86];
char aa[85],bb[85];
int na=0,nb=0;

int main()
{
	scanf("%d",&n);
	for(int i=0;i<n;i++)
	{
		na=0,nb=0;
		//配列aa(bb)を'0'で初期化
		fill(aa,aa+85,'0');
		fill(bb,bb+85,'0');
		fill(a,a+85,0);
		fill(b,b+85,0);
		fill(answer,answer+85,0);
		scanf("%s%s",a,b);
		for(int i=0;a[i]!='\0';i++)
		{
			na++;
		}
		for(int i=0;b[i]!='\0';i++)
		{
			nb++;
		}
		//配列a(b)を右詰めでaa(bb)に収納する
		memcpy(aa+85-na,a,sizeof(char)*na);
		memcpy(bb+85-nb,b,sizeof(char)*nb);
		//以下足し算
		for(int j=84;j>=0;j--)
		{
			answer[j]+=aa[j]+bb[j]-'0';
			//繰り上げ
			if(answer[j]>'9')
			{
				answer[j-1]++;
				answer[j]-=10;
			}
		}
		int count=0;
		for(int j=0;(j<84)&&answer[j]=='0';j++)
		{
			count++;
		}
		if(count<5)
		{
			printf("overflow\n");
		}
		else
		{
		answer[85]='\0';//文字列終了のお知らせ
		memcpy(answer,answer+count,85-count+1);
		//出力
		printf("%s\n",answer);
		}
	}
	return 0;
}

C++: #include<iostream>
#include<string>
#include<algorithm>
using namespace std;
string* sum (string& a, string& b);

int main(){
  string a1 = "", a2 = "", *sum0;
  int n, A1, A2;

  cin >> n;
  for(int i = 0; i < n ; i++){
    cin >> a1 >> a2;
    reverse(a1.begin(), a1.end());
    reverse(a2.begin(), a2.end());
    A1 = a1.length();
    A2 = a2.length();
    if(A1 < A2) {
      swap (A1, A2);
      swap (a1, a2);
    }

    for(int i = 0; i < A1 - A2; i++)   a2 += '0';

    sum0 = sum(a1, a2);

    if (sum0->length() > 80) sum0 = new string("overflow");
    else  reverse(sum0->begin(), sum0->end());
    
    cout << *sum0 <<endl;
  }
}

string* sum(string& a, string& b){
  static string buff = "";
  int x = 0, y ;
  for(int i = 0; i < a.length(); i++){
    y = a[i] - '0' + b[i] - '0';
    if (y + x > 9){
      buff += (y + x)% 10 + '0';
      x = 1;
    } else {
      buff += y + x+ '0';
      x = 0;
    }
  }
  if (x==1) buff += '1';
  return &buff;
}

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

using namespace std;
int main(){
	int n,l,m,c;
	string a,b;
	cin >> n;
	for(int i=0;i<n;i++){
		char s[90] = {0};
		cin >> a;
		cin >> b;
		reverse(a.begin(),a.end());
		reverse(b.begin(),b.end());
		if(a.length()<b.length())swap(a,b);
		l = a.length();
		m = b.length();
		c=0;
		for(int j=0;j<l;j++){
			int o=a[j]-'0' + c;
			if(j<m)o += b[j]-'0';
			c = o>9;
			s[j] = o%10 + '0';
		}
		if(c>0)s[l++]='1';
		reverse(s,s+l);
		if(l>80)cout << "overflow" << endl;
		else printf("%s\n",s);
	}
	return 0;
}

C++: #include <stdio.h>
#include <stdlib.h>
#include <string.h>

void ctod(char *c, int *d){
	int len = strlen(c);
	char ct[10];
	int h = len / 9;
	int a = len % 9;

	for(int i=0;i<9;++i){
		d[i] = 0;
	}
	if(a != 0){
		memcpy(ct, c, a);
		ct[a] = '\0';
		d[h] = atoi(ct);
	}

	for(int i=0; i<h; ++i){
		memcpy(ct, c + len - 9*(i + 1), 9);
		ct[9] = '\0';
		d[i] = atoi(ct);
	}
}

void dtoc(char *c, int *d){
	char ct[10];
	int m = -1;
	int o = 0;
	for(int i=8; i>=0; --i){
		if(d[i] != 0){
			m = i;
			break;
		}
	}
	if(m == -1){
		c[0] = '0';
		c[1] = '\0';
		return;
	}

	sprintf(c, "%d", d[m]);
	o = strlen(c);
	for(int i = m-1; i>=0; --i){
		sprintf(c+o, "%09d", d[i]);
		o += 9;
	}
}

void add(int *d1, int *d2, int *d){
	int s = 0;
	for (int i=0; i<9; ++i){
		d[i] = d1[i] + d2[i] + s;
		s = d[i] / 1000000000;
		if(s > 0){
			d[i] -= 1000000000;
		}
	}
}

int main(void){
	int n = 0;
	char i1[100], i2[100], o[100];
	int d1[9], d2[9], d[9];

	scanf("%d", &n);
	for(int i=0; i<n; ++i){
		scanf("%s", i1);
		scanf("%s", i2);
		if(strlen(i1) > 80 || strlen(i2) > 80){
			puts("overflow");
			continue;
		}

		for(int j=0; j<9;++j){
			d1[j] = d2[j] = d[j] = 0;
		}
		ctod(i1, d1);
		ctod(i2, d2);
		add(d1, d2, d);
		dtoc(o, d);
		if(strlen(o) > 80){
			puts("overflow");
			continue;
		}
		printf("%s\n", o);
	}
	return 0;
}