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<bits/stdc++.h>
using namespace std;

struct Integer{
    int num[100];
    Integer(const char *s){
        fill_n(num,100,0);
        int l=strlen(s);
        for(int i=0;i<l;i++){
            num[l-i-1]=s[i]-'0';
        }
    }
};
const Integer operator+(const Integer &lint,const Integer &rint){
    Integer ret("0");

    for(int i=0;i<100;i++){
        int v=ret.num[i]+lint.num[i]+rint.num[i];
        ret.num[i]=v%10;
        if(i+1>=100)continue;
        ret.num[i+1]+=v/10;

    }
    return ret;
}

char a[200],b[200];
int main(){
    int n;
    scanf("%d",&n);
    while(n--){
        scanf("%s%s",a,b);
        Integer ans=Integer(a)+Integer(b);
        int s=0;
        for(int i=0;i<100;i++)if(ans.num[i])s=i;
        if(s+1>=80){
            puts("overflow");
            continue;
        }
        for(int i=s;i>=0;i--)printf("%d",ans.num[i]);
        puts("");
    }
    return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
using namespace std;
static const double EPS = 1e-5;
typedef long long ll;
typedef pair<int,int> pint;
#define rep(i,n) for(int i=0;i<n;i++)
#define F first
#define S second
int dx[]={1,-1,0,0},dy[]={0,0,1,-1};

int m;

int f(string s1,string s2,int x){
	if(m>80){cout<<"overflow"<<endl;return 0;}
	if(s1.size()<=m&&s2.size()<=m&&x==0)return 0;
	if(s1.size()>m)x+=s1[s1.size()-m-1]-'0';
	if(s2.size()>m)x+=s2[s2.size()-m-1]-'0';
	++m;
	f(s1,s2,x/10);
	if(m<=80)cout<<x%10;
	return 0;
}

int main(){
	int n;
	cin>>n;
	rep(i,n){
		m=0;
		string s1,s2;
		cin>>s1>>s2;
		f(s1,s2,0);
		cout<<endl;
	}
	return 0;
}

C++: #include<iostream>
#include<string>
#include<vector>
using namespace std;
int main() {
	int n,i,j,k,s,t,u;
	int carry = 0;
	string a, b,d;
	vector<int> c;
	cin >> n;
	for (i = 0; i < n; i++) {
		c.clear();
		cin >> a;
		cin >> b;
		while (a.size() > 80 || b.size() > 80) {
			cout << "overflow" << endl;
			break; break;
		}
		while (a.size() > b.size()) {
			b = "0" + b;
		}
		while (b.size() > a.size()) {
			a = "0" + a;
		}
		s = a.size();
		for (j = s-1; j >=0; j--) {
			t = a[j]-'0' + b[j]-'0';
			if (carry == 1) {
				carry = 0;
				t += 1;
			}
			while (t >= 10) {
				t -= 10;
				carry += 1;
			}
			c.push_back(t);
		}
		while (carry == 1) {
			carry = 0;
			c.push_back(1);
		}
		u = c.size();
		if (u > 80) {
			cout << "overflow" << endl;
			break;
		}
		for (k = u - 1; k >= 0; k--) {
			 cout << c[k];
		}
		cout << endl;
	}
	return 0;
}

C++: #include<stdio.h>

int main(){
	char x[100], y[100], z[100];
	int n, xl, yl, zl;
	int i;

	scanf("%d",&n);
	for(i=0;i<n;i++){
		scanf("%s",x);
		scanf("%s",y);
		for(xl=0;x[xl]!='\0';xl++) x[xl]-='0';
		for(yl=0;y[yl]!='\0';yl++) y[yl]-='0';
		xl--;
		yl--;
		if(xl>80 || yl>80){
			printf("overflow\n");
			continue;
		}

		for(zl=0;zl<100;zl++) z[zl]=0;
		for(zl=0;xl>=0 || yl>=0;zl++){
			if(xl>=0) z[zl]+=x[xl--];
			if(yl>=0) z[zl]+=y[yl--];
			if(z[zl]>=10){
				z[zl]-=10;
				z[zl+1]++;
			}
		}

		for(zl=99;z[zl]==0;zl--){}
		if(zl>80){
			printf("overflow\n");
			continue;
		}
		for(xl=0;zl>=0;zl--) x[xl++]=(z[zl]+'0');
		x[xl] = '\0';
		printf("%s\n",x);
	}
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;

int main()
{
  int N;
  char str1[81];
  char str2[81];
  char s1[81];
  char s2[81];
  cin >> N;
  for(int i = 0; i < N; i++){
    cin >> str1;
    cin >> str2;
    int m1 = strlen(str1), m2 = strlen(str2);
    if(m1 > 80 || m2 > 80)
      cout << "overflow" << endl;
    else if(atoi(str1) + atoi(str2) < 2147483647 && atoi(str1) + atoi(str2) > 0)
      cout << atoi(str1) + atoi(str2) << endl; 
    else{
      if(m1 > m2){
	for(int i = 0; i < m1 - m2 + 1; i++)
	  s1[i] = '0';
	s1[m1 - m2] = '\0';
	strcat(s1, str2);
	strcpy(s2, str1);
      }else if(m2 > m1){
	for(int i = 0; i < m2 - m1; i++)
	  s2[i] = '0';
	s2[m2 - m1] = '\0';
	strcat(s2, str1);
	strcpy(s1, str2);
      }else{
	strcpy(s1, str2);
	strcpy(s2, str1);
      }
      int ans[81];
      int n = 0;
      for(int i = ((m1 > m2) ? m1 : m2) - 1; i >= 0; i--, n++)
	if((s1[i] - '0') + (s2[i] - '0') >= 10){
	  s1[i - 1] = s1[i - 1] + 1;
	  ans[i] = (s1[i] - '0') + (s2[i] - '0') - 10;
	}else
	  ans[i] = (s1[i] - '0') + (s2[i] - '0');
      if(n > 80)
	cout << "overflow" << endl;
      else{
	if((s1[0] - '0') + (s2[0] - '0') >= 10)
	  cout << "1";
	for(int i = 0; i < ((m1 > m2) ? m1 : m2); i++)
	  cout << ans[i];
      }
    }
    cout << endl;
  }
}