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 <vector>
#include <cstdio>
#define N 10000
using namespace std;

char s[N];
vector<int> a,b;
int n, an,bn;

void pr( vector<int> aa ){
  unsigned int i=0, len;
  while( aa[i]==0 ) i++;

  len = aa.size()-i;
  //  cout << "length : "<< len << endl;
  if( len>80 ){
    cout << "overflow" << endl;
  }else{
    for( ;i<aa.size();i++ )
      cout << aa[i];
    cout << endl;
  }
}

int main(){
  cin >> n;
  fgets( s,N,stdin );
  for( int loop=0;loop<n;loop++ ){

    a.clear();
    fgets( s,N-1,stdin );    
    for( int i=0; s[i]!='\n'&& s[i]!='\0' ;i++ )
      a.push_back( s[i]-'0' );

    b.clear();
    fgets( s,N,stdin );
    for( int i=0; s[i]!='\n'&& s[i]!='\0' ;i++ )
      b.push_back( s[i]-'0' );

    an=a.size(); bn=b.size();
    while( an>bn ){
      b.insert( b.begin(),1, 0 ); bn++;
    }
    while( an<bn ){
      a.insert( a.begin(),1, 0 ); an++;
    }
    //    pr(a);
    //    pr(b);
    a.insert( a.begin(),1,0 );
    b.insert( b.begin(),1,0 );
    for( int i=an;i>=0;i-- ){
      a[i] = a[i] + b[i];
      while( a[i]>=10 ){
	a[i]-=10; a[i-1]++;
      }
    }
    pr( a );
  }
  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;
		}
		for (k = u - 1; k >= 0; k--) {
			 cout << c[k];
		}
		cout << endl;
	}
	return 0;
}

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

int main(){
	int n;
	cin >> n;
	while( n-- > 0 ){
		string num1, num2;
		cin >> num1 >> num2;
		char sum[101];
		int degit = 0;
		for( int i = 0; i < 101; i++ ) sum[i] = '0';
		for( int i = 0; i < num1.size(); i++ ){
			sum[100-i] = num1[num1.size()-i-1];
		}
/*
		int d;
		for( int i = 0; i < num1.size() || i < num2.size() || degit != 0; i++ ){
			int now;
			if( i < num2.size() ){
				now = (int)(sum[100-i]-'0') + (int)(num2[num2.size()-i-1]-'0') + degit;
			}else{
				now = (int)(sum[100-i]-'0') + degit;
			}
			sum[100-i] = (char)(now%10)+'0';
			if( now >= 10 ) degit = 1;
			else degit = 0;
			d = i;
		}
		*/
		int d = 3;
		if( d < 80 ){
			for( int i = 100-d; i < 101; i++ ) cout << sum[i];
			cout << endl;
		}else{
			cout << "overflow" << endl;
		}
	}
}

C++: #include <cstdio>
#include <cstring>
#include <iostream>

using namespace std;

const int N = 85;

char a[N], b[N];

void reverse(char a[]) {
	int len = strlen(a);
	for (int i=0, j=len-1; i<j; ++i, --j) {
		char tmp = a[i];
		a[i] = a[j];
		a[j] = tmp;
	}
}

void add(char a[], char b[]) {
	int lenA = strlen(a);
	int lenB = strlen(b);
	int i, j, tmp, jin = 0;
	for (i=0; i<lenA && i<lenB; ++i) {
		tmp = (a[i] - '0') + (b[i] - '0') + jin;
		a[i] = tmp % 10 + '0';
		jin = tmp / 10;  
	}
	if (!a[i] && !b[i] && jin) {
		a[lenA] = jin + '0';
		a[lenA + 1] = '\0';
	}
	else if (a[i] && !b[i] && jin) {
		for (; i<lenA; ++i) {
			tmp = a[i] - '0' + jin;
			a[i] = tmp % 10 + '0';
			jin = tmp / 10;
		}
		if (jin) {
			a[lenA] = jin + '0';
			a[lenA + 1] = '\0';
		} 
	}
	else if (!a[i] && b[i] && jin) {
		for (; i<lenB; ++i) {
			tmp = b[i] - '0' + jin;
			a[i] = tmp % 10 + '0';
			jin = tmp / 10;
		}
		if (jin) {
			a[lenB] = jin + '0';
			a[lenB + 1] = '\0';
		}
		else a[lenB] = '\0';
	}
}

int main() {
	int t;
	scanf ("%d", &t);
	while (t--) {
		scanf ("%s%s", a, b);
		reverse(a);
		reverse(b);
		add(a, b);
		if (strlen(a) > 80) printf ("overflow\n");
		else reverse(a), printf ("%s\n", a);
	}
}

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";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;
}