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;
            if(in.size() > 80){ res[80] = 1; break; }
            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++: #define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>
#include <string.h>

using namespace std;

const size_t opsize = 81, bufsize = 102;
unsigned char op1[opsize], op2[opsize];
char buf[bufsize];

bool readOp(unsigned char * op){
    memset(op, 0, opsize);
    
    fgets(buf, bufsize, stdin);
    int l = strlen(buf);
    if(l > 81) return true;

    char *p = &buf[l-2];
    for (int j = 0; j < l-1; j++) {
        op[j] = *p - '0';
        p--;
    }
    return false;
}

void printOp(unsigned char * op){
    int mh = opsize - 1;
    while(op[mh] == 0 && mh > 0) mh--;
    for(; mh >= 0; mh--){
        putchar(op[mh] + '0');
    }
    putchar('\n');
}

bool plus(){
    for (int i = 0; i < opsize - 1; i++) {
        op1[i] += op2[i];
        if(op1[i] >= 10){
            op1[i] -= 10;
            op1[i+1] += 1;
        }
    }
    return op1[opsize - 1] != 0;
}

int main(int argc, char const* argv[])
{
    int n;
    scanf("%d ", &n);
    for (int i = 0; i < n; i++) {
        bool overflow = false;
        overflow |= readOp(op1);
        overflow |= readOp(op2);
        if(overflow){
            puts("overflow");
            continue;
        }
        overflow = plus();

        if(overflow){
            puts("overflow");
            continue;
        }
        printOp(op1);
    }
    
    return 0;
}

C++: #include<iostream>
#include<stdio.h>
#include <algorithm>
#include <utility>
using namespace std;
using namespace std;
int main(){
	
	int m;
	char in[2][100];
	char ans[100];
	int ie[2];
	int ien[2];
	bool max10;
	int Min;
	bool NMin;
	scanf("%d",&m);
	for(;m--;){
		
		for(int i=0;i<2;i++){
			scanf(" %s",&in[i]);
		}
		for(int i=0;i<2;i++){
			for(ie[i]=0;in[i][ie[i]]!='\0';ie[i]++){
				in[i][ie[i]]=in[i][ie[i]]-'0';
			}
		}
		ie[0]--;
		ie[1]--;
		Min=max(ie[0],ie[1]);
		if((Min>79)||((Min>78)&&(ie[0]==ie[1])&&((int(in[0][0])+int(in[1][0]))>9))){
			cout<<"overflow"<<endl;
		}else{	
			if(ie[0]>ie[1]){
				NMin=0;
			}else{
				NMin=1;
			}
			ien[0]=ie[0];
			ien[1]=ie[1];
			for(;min(ien[0],ien[1])+1;ien[0]--,ien[1]--){
				in[NMin][ien[NMin]]=in[0][ien[0]]+in[1][ien[1]];
				if(in[NMin][ien[NMin]+1]>9){
					in[NMin][ien[NMin]+1]-=10;
					in[NMin][ien[NMin]]  +=1;
				}
			}
			max10=0;
			
			for(;ien[NMin]>-1;ien[NMin]--){
				in[NMin][ien[NMin]]=in[NMin][ien[NMin]];
				if(in[NMin][ien[NMin]+1]>9){
					in[NMin][ien[NMin]+1]-=10;
					in[NMin][ien[NMin]]  +=1;
				}
			}
			for(int j=0;j<ie[NMin]+1;j++){
				in[NMin][j]=in[NMin][j]+'0';
			}
			
			
			if(max10) cout<<"1";
			cout<<in[NMin]<<endl;
		}
	}
	return 0;
}

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

#define rep2(x,from,to) for(int x=(from);(x)<(to);(x)++)
#define rep(x,to) rep2(x,0,to)
int main() {
	int n;
	cin >> n;
	while(n--) {
		char a[84], b[84];
		int x[84], y[84], s[84], max;
		cin >> a >> b;
		int i = 0, j = 0;
		for(; a[i] != '\0'; ++i) {
			x[i] = a[i] - '0';
		}
		for(; b[j] != '\0'; ++j) {
			y[j] = b[j] - '0';
		}
		if(i > 80 || j > 80) {
			cout << "overflow" << endl;
			break;
		}
		if(i > j) {
			for(int k = j - 1; k >= 0; k--) {
				y[i-j+k] = y[k];
			}
			rep(k,i-j) {
				y[k] = 0;
			}
			max = i;
		} else if(i < j) {
			for(int k = i - 1; k >= 0; k--) {
				x[j-i+k] = x[k];
			}
			rep(k,j-i) {
				x[k] = 0;
			}
			max = j;
		} else max = i;
		bool f = 0;
		for(int k = max - 1; k >= 0; k--) {
			int c = x[k] + y[k];
			if(f) c++;
			if(c >= 10) {
				f = 1, c -= 10;
			} else f = 0;
			s[k] = c;
		}
		if(f) {
			max++;
		}
		if(max > 80) cout << "overflow" << endl;
		else {
			if(f) {
				cout << 1;
				max--;
			}
			rep(k,max) {
				cout << s[k];
			}
			cout << endl;
		}
	}
	return 0;
}