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 <algorithm>
#include <set>
#include <queue>
#include <stack>
#include <string>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
 
#define rep(i, n) for(int i = 0; i < n; i ++)
#define ALL(T) T.begin(), T.end()
#define mp make_pair
#define pb push_back
#define MEMSET(v, h) memset((v), h, sizeof(v))
 
using namespace std; 

typedef pair<int, int> pii;
typedef long long ll;
typedef vector<int> vi;
typedef vector<string> vs;

const int INF = 1 << 24;
 
int main(void){
    int n; cin >> n;

    while(n --){
        vi res(81);
        rep(i, 2){
            string in; cin >> in;
            rep(j, in.size() + 1){
                if(j != in.size()) res[j] += in[in.size() - j - 1] - '0';
                for(int l = 0; res[j + l] > 9; l ++) res[j + l + 1] ++, res[j + l] %= 10;
            }
        }

        if(res[80]){ cout << "overflow" << endl; continue; }

        bool ok = false;
        for(int i = 79; i >= 0; i --){
            if(!ok) if(res[i]) ok = true;
            if(ok) cout << res[i];
        }
        cout << endl;
    }
 
    return 0;
}

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

using namespace std;

int main(){
    int n; cin >> n;
    while(n--){
        string a,b;
        cin >> a >> b;
        reverse(a.begin(), a.end());
        reverse(b.begin(), b.end());
        if(b.size() < a.size()) swap(a,b);
        b += "0";
        for(int i=0; i<b.size()-1; i++){
            int aa = i < a.size() ? a[i] - '0' : 0;
            int bb = b[i] - '0';
            int cc = aa + bb;
            b[i] = (cc%10) + '0';
            //cout << aa << "+" << bb << "=" << cc << endl;
            if(cc >= 10){
                b[i+1]++;
            }
        }
        if(b[b.size()-1] == '0')
            b = string(b.begin(), b.end()-1);
        reverse(b.begin(), b.end());
        cout << b << endl;
    }
    return 0;
}

C++: #include <stdio.h>
#include <string.h>
 
int main(void) {
    char a[200],b[200],result[200],temp[200];
    int ketaagari;
    int i,j;
    int max;
    char in;
    int overflow;
    int count,kazu;
    scanf("%d",&kazu);
    for(count=0;count<kazu;count++) {
        for(i=0;i<200;i++) {
            a[i]=0;b[i]=0;
        }
        i=0;
        overflow=0;
    	
    	scanf(" %s ",temp);
    	
    	i=strlen(temp);
    	if(i>80)overflow=1;
        for(j=0;j<i;j++)a[j]=temp[i-j-1]-'0';
    	scanf(" %s ",temp);
    	i=strlen(temp);
    	if(i>80)overflow=1;

    	for(j=0;j<i;j++)b[j]=temp[i-j-1]-'0';
 
        for(i=0,ketaagari=0,max=0;i<80;i++) {
            result[i]=(a[i]+b[i]+ketaagari)%10;
            ketaagari=(a[i]+b[i]+ketaagari)/10;
            if(result[i]!=0)max=i;
        }
        if(ketaagari)overflow=1;

    	if(overflow==0) {
            for(i=max;i>=0;i--)printf("%d",result[i]);
            printf("\n");
        } else printf("overflow\n");
    }
    return 0;
}

C++: #include <iostream>
#include <string>
#define MAX 80

using namespace std;

int main()
{
	int n;
	cin >> n;
	for (int counter = 0; counter < n; counter++){
		string a, b;
		cin >> a >> b;
		if (a.length() > MAX || b.length() > MAX){
			cout << "overflow" << endl;
			continue;
		}
		int inta[MAX + 2], intb[MAX + 2], sum[MAX + 2];
		fill(inta, inta + MAX + 2, 0);
		fill(intb, intb + MAX + 2, 0);
		fill(sum, sum + MAX + 2, 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 < MAX + 2; i++){
			sum[i] = inta[i] + intb[i] + over;
			if (sum[i] >= 10){
				sum[i] %= 10;
				over = 1;
			}
			else{
				over = 0;
			}
		}

		for (int i = MAX + 1;; i--){
			if (sum[i] != 0){
				if (i >= MAX){
					cout << "overflow" << endl;
					break;
				}
				for (int j = i; j >= 0; j--){
					cout << sum[j];
				}
				cout << endl;
				break;
			}
		}
	}
	return 0;
}

C++: #include <stdio.h>
#include <string.h>
int main(void){
    int n,ap,bp,cp,t;
    char a[81],b[81],c[81];
    scanf("%d",&n);
    while(~scanf("%s%s",&a,&b)){
        ap=strlen(a);
        bp=strlen(b);
        cp=sizeof(c)-1;
        c[cp]='\0';
        t=0;
        while((t||ap||bp)&&cp>0){
            t+=(ap?a[--ap]-'0':0)+(bp?b[--bp]-'0':0);
            c[--cp]='0'+(t%10);
            t/=10;
        }
        if(t)printf("overflow\n");
        else printf("%s\n",&c[cp]);
    }
    return 0;
}