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<algorithm>
#include<string>
#include<cstring>
using namespace std;
int main(){

	int n;
	cin >> n;
	while(n > 0){
        char a[120] = {0};
        char b[120] = {0};
        scanf("%s%s",a,b);
        char ans[120] = {0};
        for(int i = 0; i < strlen(a)/2; i++){
            swap(a[i],a[strlen(a)-i-1]);
        }
        for(int i = 0; i < strlen(b)/2; i++){
            swap(b[i],b[strlen(b)-i-1]);
        }
        int len = max(strlen(a),strlen(b));
        for(int i = 0; i < len; i++){
            if(ans[i] != 0){
                if(a[i] == 0 || b[i] == 0)
                    ans[i] += a[i] + b[i] - '0';
                else ans[i] += a[i] + b[i] - '0' - '0';

            }
            else if(a[i] == 0 || b[i] == 0) ans[i] += a[i] + b[i];
            else ans[i] += a[i] + b[i] - '0';
            if(ans[i] >= 58){
                ans[i+1]+='1';
                ans[i] -= 10;
            }
        }
        for(int i = 0; i < strlen(ans)/2; i++){
            swap(ans[i],ans[strlen(ans)-i-1]);
        }
        int Len_a = 0,Len_b = 0,Len_ans = 0;
        for(int i = 0; a[i] != 0; i++) Len_a++;
        for(int i = 0; b[i] != 0; i++) Len_b++;
        for(int i = 0; ans[i] != 0; i++) Len_ans++;
        if(Len_a > 80 || Len_b > 80 || Len_ans > 80) printf("overflow");
        else for(int i = 0; ans[i] != 0; i++) printf("%c",ans[i]);
        printf("\n");
        n--;
	}

	return 0;
}

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

int main(){
	int n;
	cin >> n;
	for(int j=0;j<n;j++){
		char a[81],b[81],c[81];
		int ka = 0;
		int kb = 0;
		int kc = 0;
		bool ovf = false;
		cin >> a[ka];
		ka++;
		while(1){
			scanf("%c",&a[ka]);
			if(ka==80 and a[ka]!='\n') ovf = true;
			if(a[ka]=='\n' or ovf) break;
			ka++;
		}
		while(1){
			scanf("%c",&b[kb]);
			if(kb==80 and b[kb]!='\n') ovf = true;
			if(b[kb]=='\n' or ovf) break;
			kb++;
		}
		int k = 0;
		char t;
		for(int i=0;i<81;i++){
			if(ka<=i and kb<=i){
				if(k==1){
					sprintf(&c[i],"%d",k);
					kc++;
					if(i==80) ovf = true;
					break;
				}
			}
			int ia = 0;
			t = a[ka-i-1];
			if(ka>=i) ia = atoi(&t);
			int ib = 0;
			t = b[kb-i-1];
			if(kb>=i) ib = atoi(&t);
			int s = ia + ib + k;
			k = 0;
			if(s>9){ k = 1; s = s%10;}
			sprintf(&c[i],"%d",s);
			kc++;
		}
		if(ovf) cout << "overflow" << endl;
		else{
			for(int i=kc-1;i>=0;i--) cout << c[i];
			cout << endl;
		}
	}
}

C++: #include<stdio.h>
#include<iostream>
#include<string>
using namespace std;
int main(){

int n;
cin>>n;
for(int iii=0;iii<n;iii++){
string st1,st2;
int n1[82]={},n2[82]={};
cin>>st1>>st2;
for(int i=0;i<st1.size();i++)
n1[i]=st1[st1.size()-i-1]-'0';
for(int i=0;i<st2.size();i++)
n2[i]=st2[st2.size()-i-1]-'0';
int N[82]={};int y=0;

int r=st1.size();
if(r<st2.size())r=st2.size();
for(int i=0;i<r;i++){
N[i]=(n1[i]+n2[i]+y)%10;
y=(n1[i]+n2[i]+y)/10;
if(i==r-1&&y>0)r++;
}
if(r>80)cout<<"overflow"<<endl;
else{
for(int i=0;i<r;i++)
cout<<N[r-i-1];
cout<<endl;
}}
return 0;
}

C++: #include <iostream>
#include <string.h>

using namespace std;

int main(void){
	int n;

	cin >> n;
	for(int i=0;i<n;i++){
	}

	return 0;
}

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

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

    cin >> num1;
    cin.clear();
    cin >> num2;
    cin.clear();
    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;
}