Go: package main

import (
	"bufio"
	"os"
	"fmt"
	"strings"
)

var scanner = bufio.NewScanner(os.Stdin)

func main() {
	var n int
	fmt.Scan(&n)
	for i := 0; i < n; i++ {
		scanner.Scan()
		s := scanner.Text()
		rs := []rune(s)
		flag := false
		for b := 0; b <= 26; b++ {
			for a := 0; a <= 26; a++ {
				ans := rs
				if a%2 != 0 && a%13 != 0 {
					for j := 0; j < len(ans); j++ {
						if ans[j] >= 'a' && ans[j] <= 'z' {
							ans[j] = 'a' + ('a'*(ans[j]-'a')+'b')%26
						}
					}
					sans := runeSlice2String(ans)
					if strings.Contains(sans, "that") || strings.Contains(sans, "this") {
						fmt.Println(sans)
						flag = true
						break
					}
				}
			}
			if flag {
				break
			}
		}
	}
}

func runeSlice2String(input []rune) string {
	tmp := make([]string, len(input))
	for i := 0; i < len(input); i++ {
		tmp[i] = string(input[i])
	}
	return strings.Join(tmp, "")
}

C++: #include <iostream>
#include <cstdio>
#include <algorithm>
#include <cassert>
#include <vector>
#include <string>
#include <cmath>
#include <map> 
#include <sstream>
#include <cstdio>
#include <complex>
#include <cstring>
using namespace std;
 
const int MAX= 10000100;

#define loop(i,a,b) for(int i = a ; i < b ; i ++)
#define rep(i,a) loop(i,0,a)
#define all(a) (a).begin(),(a).end()
#define ll long long int
#define gcd(a,b) __gcd(a,b)
#define pb(a) push_back(a)
int GCD(int a, int b) {if(!b) return a; return gcd(b, a%b);}
int lcm(int a, int b) {return a*b / gcd(a, b);}

char change(int a,int b, char c){
  if(c == ' ')return c;
  return 'a' + (a * (c - 'a') + b) % 26;
}
int main(void){
  int a[] = {1,3,5,7,9,11,15,17,19,21,23,25,0};
  int n; cin>>n; cin.ignore();
  string str,str_cp,sp = " ";
  
  while(getline(cin,str)){
    str = str_cp = sp + str + sp;
    bool f = false;
    for(int i = 0 ; !f && a[i] ; i ++){
      for(int b = 0 ; !f && b < 26 ; b ++){
	for(int j = 0 ; j < str.length() ; j ++){
	  str[j] = change(a[i],b,str[j]);
	}
	if(str.find(" that ") != string::npos
	   || str.find(" this ") != string::npos){
	  f = true;
	  break;
	}

	str = str_cp;
      }
    }
    cout<<str.substr(1,str.length() - 2)<<endl;
  }
}

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

using namespace std;

int gcd(int x,int y){
  if(y == 0)return x;
  return gcd(y,x%y);
}

int lcm(int x,int y){
  return (x*y)/gcd(x,y);
}

string affine(string s,int a,int b){
  string news;
  for(int i=0;i<s.length();i++){
    if(!('a'<= s[i] && s[i]<='z') ){
      news+=s[i];
      continue;
    }
    int y = s[i]-'a';
    news+= (char)((a*y+b)%26+'a');
  }
  
  return news;
}


int main(){

  int N;
  string s;
  cin >> N;
  cin.ignore();
  while(N-- > 0){
    getline(cin,s,'\n');
   
    bool fin = false;
    for(int a=0;a<=100;a++){
      if(gcd(a,26) == 1){
	for(int b=0;b<=27;b++){
	  string Ns = affine(s,a,b);	  
	  if(Ns.find("that") != string::npos || Ns.find("This") != string::npos){
	    cout << Ns << endl;
	    fin = true;
	    break;
	  }
	}

	}
	if(fin)break;
    }
    if(!fin)cout << s << endl;


  }
  return 0;
}

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

int main(){
	int n;
	string str;
	bool output;
	int code;
	int str1[4] = {19, 7, 8, 18};
	int str2[4] = {19, 7, 0, 19};
	
	cin >> n;
	
	getline(cin, str);
	for(int i = 0; i < n; i++){
		getline(cin, str);
		
		output = false;
		
		for(int a = 0; !output && a < 26; a++){
			for(int b = 0; !output && b < 26; b++){
				for(int p = 0; !output && p < str.size() - 4; p++){
					for(int c = 0; c < 4; c++){
						code = (a * (str[p + c]-97) + b) % 26;
						if(code != str1[c]) break;
						else if(c + 1 == 4){
							output = true;
							for(int P = 0; P < str.size(); P++){
								if(str[P] != ' ') cout << (char)((a * (str[P]-97) + b) % 26 + 97);
								else cout << " ";
							}
							cout << endl;
						}
					}
					for(int c = 0; c < 4; c++){
						code = (a * (str[p + c]-97) + b) % 26;
						if(code != str2[c]) break;
						else if(c + 1 == 4){
							output = true;
							for(int P = 0; P < str.size(); P++){
								if(str[P] != ' ') cout << (char)((a * (str[P]-97) + b) % 26 + 97);
								else cout << " ";
							}
							cout << endl;
						}
					}
				}
			}
		}
	}
	
	return 0;
}

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

int main(){
	int n;
	char str[257] = {}, str_c[257], len;
	cin >> n;
	//getchar();
	fflush(stdin);
	for (int m = 0; m < n; m++){
		gets(str);
		len = strlen(str);
		//printf("%d\n", len);
		for (int i = 0; i < 26; i++){
			/*if (i % 2 == 0 || i % 13 == 0) continue;*/
			for (int j = 0; j < 26; j++){
				for (int k = 0; k <= len; k++){
					if (isalpha(str[k])){
						str[k] -= 'a';
						str_c[k] = (str[k] * i + j) % 26 + 'a';
						str[k] += 'a';
					}
					else{
						str_c[k] = str[k];
					}
				}
				if (strstr(str_c, "this") || strstr(str_c, "that")){
					printf("%s\n", str_c);
					return 0;
				}
			}
		}
	}
	return 0;
}

C++: #include<iostream>
#include<map>
#include<string>
#include<vector>
#include<algorithm>
#include<numeric>
#include<cmath>
using namespace std;
int inf = 1000000000;

char affine(char c, int a, int b){
  int x = c - 'a';
  int y = ( a * x + b ) % 26;
  char r = 'a' + y;
  return r;
}

int main(){

  int n;
  cin >> n;
  cin.ignore();
  for(int l=0; l<n; l++){
    string s;
    getline(cin, s);

    for(int i=0; i<30; i++){
      for(int j=0; j<30; j++){
        string t = "";
        for(int k=0; k<s.size(); k++){
          if( 'a' <= s[k] && s[k] <= 'z' ) t += affine(s[k], i, j);
          else t += s[k];
        }
        // cout << t << endl;
        for(int k=0; k<t.size()-4; k++){
          if( (t[k] == 't' && t[k+1] == 'h' && t[k+2] == 'a' && t[k+3] == 't') || (t[k] == 't' && t[k+1] == 'h' && t[k+2] == 'i' && t[k+3] == 's') ) cout << t << endl;
        }
      }
    }

  }


  return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cstdlib>
#include <cstdio>
using namespace std;
#define M_PI 3.141592
#define toRad 2.0*M_PI/360.0
#define inin(x) int x;cin>>x;
#define all(x) x.begin(),x.end()
#define debug(x) cout<<#x<<" "<<x<<endl;
int euclid(int a, int b)
{
	if (a < b)swap(a, b);
	if (b == 0)return a;
	else return euclid(b, a%b);
}
char hoge(int a)
{
	return 'a' + a;
}
bool check(string a)
{
	if (a.find("that", 0) != string::npos||a.find("this",0)!=string::npos)
	{
		return true;
	}
	return false;
}
int main()
{
	int n;
	cin >> n;
	cin.ignore();
	while (n--)
	{
		string a;
		bool ok = true;
		getline(cin, a);
		cout << a << endl;
		for (int i = 0;ok; i++)
		{
			if (euclid(i, 26) != 1)continue;
			for (int l = 0; l <= 25&&ok; l++)
			{
				for (int k = 0; k <= 25&&ok; k++)
				{
					int j = (i*l + k)%26;
					if (hoge(j) == a[0])
					{
						string ans = "";
						for (int o = 0; o < a.size(); o++)
						{
							if ('a' <= a[o] && a[o] <= 'z')
							{
								for (int u = 0; u <= 25; u++)
								{
									int h = i*u + k;
									h %= 26;
									if (hoge(h) == a[o])
									{
										ans += hoge(u);
										break;
									}
								}
							}
							else
							{
								ans += " ";
							}
						}
						if (check(ans))
						{
							cout << ans << endl;
							ok = false;
						}
					}
				}
			}
		}

	}
}