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>
#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);
		if (strlen(a) > 80 || strlen(b) > 80) printf ("overflow\n");
		else {
			reverse(a);
			reverse(b);
			add(a, b);
			if (strlen(a) > 80) printf ("overflow\n");
			else reverse(a), printf ("%s\n", a);
		}
	}
}

C++: #include <iostream>
#include <algorithm>
#include <cctype>
#include <cstdio>
#include <math.h>
#include <map>
#include <queue>
#include <string>
using namespace std;

int N,ans[82],a,b,la,lb,up,deg;
string sta,stb;

int main(){
	cin>>N;
	for(int i=0;i<N;i++){
		cin>>sta>>stb;
		la=sta.size();
		lb=stb.size();
		up=0;
		deg=1;
		for(int i=0;i<max(la,lb)+1;i++){
			if(i>=la)a='0';
			else a=sta[la-1-i];
			if(i>=lb)b='0';
			else b=stb[lb-1-i];
			if(a+b+up>105){
				ans[i]=a+b+up-10-96;
				up=1;
			}
			else{
				ans[i]=a+b+up-96;
				up=0;
			}
			if(ans[i]!=0)deg=i+1;
		}
		if(deg>80)cout<<"overflow"<<endl;
		else{
			for(int i=0;i<deg;i++)cout<<ans[deg-1-i];
			cout<<endl;
		}
	}
}

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

using namespace std;
int main(){
	int n,l,m,c;
	char a[90],b[90],s[90];
	cin >> n;
	for(int i=0;i<n;i++){
		for(int j=0;j<90;j++)s[j]=0;
		scanf("%s%s",a,b);
		l = strlen(a);
		m = strlen(b);
		reverse(a,a+l);
		reverse(b,b+m);
		c=0;
		for(int j=0;j<max(l,m);j++){
			int o=c;
			if(j<l)o += a[j]-'0';
			if(j<m)o += b[j]-'0';
			c = o>9;
			s[j] = o%10 + '0';
		}
		l=max(l,m);
		if(c>0)s[l++]='1';
		reverse(s,s+l);
		if(l>80)puts("overflow");
		else puts(s);
	}
	return 0;
}

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

int main()
{
	int n;
	cin >> n;
	for (int counter = 0; counter < n; counter++){
		string a, b;
		cin >> a >> b;
		int inta[82], intb[82], sum[82];
		fill(inta, inta + 82, 0);
		fill(intb, intb + 82, 0);
		fill(sum, sum + 82, 0);
		for (int i = 0; i < (signed)a.length(); i++){
			inta[i] = a[a.length() - i - 1] - '0';
		}
		for (int i = 0; i < (signed)b.length(); i++){
			intb[i] = b[b.length() - i - 1] - '0';
		}
		
		int over = 0;
		for (int i = 0; i < 82; i++){
			sum[i] = inta[i] + intb[i] + over;
			if (sum[i] >= 10){
				sum[i] -= 10;
				over = 1;
			}
			else{
				over = 0;
			}
		}

		for (int i = 81;; i--){
			if (sum[i] != 0){
				for (int j = i; j >= 0; j--){
					cout << sum[j];
				}
				cout << endl;
				break;
			}
		}
	}
	return 0;
}