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 <algorithm>

using namespace std;

void tasu(string s1, string s2){
        int num[2][max(s1.length(), s2.length())+1];
        for(int i = 0; i < sizeof(num[0])/sizeof(int); i++){
                if(s1.length() > i){ 
                        num[0][i] = (int)s1.at(s1.length()-1-i) - (int)'0';
                }else{
                        num[0][i] = 0;
                }   
                if(s2.length() > i){ 
                        num[1][i] = (int)s2.at(s2.length()-1-i) - (int)'0';
                }else{
                        num[1][i] = 0;
                }   
        }   
        for(int i = 0; i < sizeof(num[0])/sizeof(int)-1; i++){
                num[1][i] += num[0][i];
                if(num[1][i] > 9){ 
                        num[1][i+1] += (int)(num[1][i]/10);
                        num[1][i] %= 10; 
                }   
        }   
        int keta = sizeof(num[0])/sizeof(int);
        while(keta && !num[1][keta-1]){
                keta--;
        }   
        if(keta >= 80){
                cout << "overflow" << endl;
        }else{
                while(keta--){
                        cout << num[1][keta];
                }   
                cout << endl;
        }   
}
int main(){
        int n;
        cin >> n;
        while(n--){
                string s1, s2; 
                cin >> s1 >> s2; 
                tasu(s1, s2);
        }   
}

C++: //#define _USE_MATH_DEFINES
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
//#include <iomanip>
#include <vector>
#include <string>
//#include <algorithm>
//#include <functional>
//#include <cmath>
//#include <time.h>

using namespace std;


int main(){

	int n, k1, k2, left, right, buf, flag;
	string s1, s2 , out;
	int aa1[10], aa2[10], ans[10];

	cin >> n;

	for (int i = 0; i < n; i++){
		for (int i = 0; i < 10; i++){
			aa1[i] = 0;
			aa2[i] = 0;
			ans[i] = 0;
		}
		flag = 0;

		cin >> s1 >> s2;
		k1 = s1.size();
		k2 = s2.size();

		if (k1 > 80 || k2 > 80){
			cout << "overflow" << endl;
		}
		else{
			buf = 8 - k1 % 8;
			for(int i = 0; i < buf; i++){
				s1.insert(0,"0");
			}
			buf = 8 - k2 % 8;
			for (int i = 0; i < buf; i++){
				s2.insert(0, "0");
			}
			left = s1.size()-8;
			for (int i = 0; i < 10; i++){
				aa1[i] = atoi(s1.substr(left, 8).c_str());
				left -= 8;
				if (left < 0)break;
			}
			left = s2.size() - 8;
			for (int i = 0; i < 10; i++){
				aa2[i] = atoi(s2.substr(left, 8).c_str());
				left -= 8;
				if (left < 0)break;
			}

			for (int i = 0; i < 10; i++){
				ans[i] += aa1[i] + aa2[i];
				if (ans[i] >= 100000000){
					ans[i + 1] += 1;
					ans[i] -= 100000000;
				}
			}
			if (ans[10] >= 100000000){
				cout << "overflow" << endl;
			}
			else{
				for (int i = 9; i >= 0; i--){
					if (flag == 0){
						if (ans[i] != 0){
							printf("%d",ans[i]);
							flag = 1;
						}
					}
					else{
						printf("%08d", ans[i]);
					}
				}
				cout << endl;
			}
		}

	}
	
	return 0;
}

C++: #include<stdio.h>
int nationalbudget(){
	int xsize=0,ysize=0,k=0;
	char x[101],y[101];
	scanf("%s",x);
	scanf("%s",y);
	for(int i=0;x[i]!='\0';i++){
		xsize++;
		if(i>79){
			printf("overflow\n");
			return 0;}}
	for(int i=0;y[i]!='\0';i++){
		ysize++;
		if(i>79){
			printf("overflow\n");
			return 0;}}
	if(xsize>=ysize){
		for(int i=0;i<xsize;i++){
			if(ysize-1-i>=0){
				int t=(x[xsize-1-i]-'0')+(y[ysize-1-i]-'0')+k;
				if(t>=10){
					if(i==79){
						printf("overflow\n");
						return 0;}
					else{
						k=1;
						t%=10;}}
				else k=0;
				x[xsize-1-i]=t+'0';}
			else{
				int t=(x[xsize-1-i]-'0')+k;
				if(t>=10){
					if(i==79){
						printf("overflow\n");
						return 0;}
					else{
						k=1;
						t%=10;}}
				else k=0;
				x[xsize-1-i]=t+'0';}}
		if(k==1)printf("1");
		for(int i=0;i<xsize;i++)printf("%c",x[i]);}
	else{
		for(int i=0;i<ysize;i++){
			if(xsize-1-i>=0){
				int t=(x[xsize-1-i]-'0')+(y[ysize-1-i]-'0')+k;
				if(t>=10){
					if(i==79){
						printf("overflow\n");
						return 0;}
					else{
						k=1;
						t%=10;}}
				else k=0;
				y[ysize-1-i]=t+'0';}
			else{
				int t=(y[ysize-1-i]-'0')+k;
				if(t>=10){
					if(i==79){
						printf("overflow\n");
						return 0;}
					else{
						k=1;
						t%=10;}}
				else k=0;
				y[ysize-1-i]=t+'0';}}
		if(k==1)printf("1");
		for(int i=0;i<ysize;i++)printf("%c",y[i]);}
	printf("\n");}
int main(){
	int n;
	scanf("%d",&n);
	for(int i=0;i<n;i++)nationalbudget();
	return 0;}