Language: C++

#include <stdio.h>
using namespace std;
int main() {
	string w[3]={"the","this","that"},st;
	int wn[3]={3,4,4},k,i,j,s,f;
	while(true) {
    k=0; 
	getline(cin,st);
	while(k<st.size()) {
		for (i=0;i<3;i++) {
			s=0; f=0;
			if (st.size()<k+wn[i]) break;
			for (j=0;j<wn[i]-1;j++) if ((w[i][j]-w[i][j+1])==(st[k+j]-st[k+j+1])) s++;
			if (s==wn[i]-1)  { f=1; i=5;}
		}
		if (f==1) break;
		for (k;st[k]>='a' && st[k]<='z' && k<80; k++);
		k++;
	}
	if (f==0) cout << st; else {
		for (i=0;i<st.size();i++) 
			if ((st[i]>='a' && st[i]<='z')) cout << (char)(((st[i]-st[k]+'t')-97+26) % 26 + 97) ; 
		    else cout << st[i];
	}
	cout << endl;
	}
	return 0;
	}

Compiler output:
a.cc: In function 'int main()':
a.cc:4:9: error: 'string' was not declared in this scope
    4 |         string w[3]={"the","this","that"},st;
      |         ^~~~~~
a.cc:2:1: note: 'std::string' is defined in header '<string>'; this is probably fixable by adding '#include <string>'
    1 | #include <stdio.h>
  +++ |+#include <string>
    2 | using namespace std;
a.cc:4:42: error: expected primary-expression before ',' token
    4 |         string w[3]={"the","this","that"},st;
      |                                          ^
a.cc:4:43: error: 'st' was not declared in this scope; did you mean 'std'?
    4 |         string w[3]={"the","this","that"},st;
      |                                           ^~
      |                                           std
a.cc:8:17: error: 'cin' was not declared in this scope
    8 |         getline(cin,st);
      |                 ^~~
a.cc:2:1: note: 'std::cin' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
    1 | #include <stdio.h>
  +++ |+#include <iostream>
    2 | using namespace std;
a.cc:13:54: error: 'w' was not declared in this scope
   13 |                         for (j=0;j<wn[i]-1;j++) if ((w[i][j]-w[i][j+1])==(st[k+j]-st[k+j+1])) s++;
      |                                                      ^
a.cc:20:19: error: 'cout' was not declared in this scope
   20 |         if (f==0) cout << st; else {
      |                   ^~~~
a.cc:20:19: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:22:57: error: 'cout' was not declared in this scope
   22 |                         if ((st[i]>='a' && st[i]<='z')) cout << (char)(((st[i]-st[k]+'t')-97+26) % 26 + 97) ;
      |                                                         ^~~~
a.cc:22:57: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:23:26: error: 'cout' was not declared in this scope
   23 |                     else cout << st[i];
      |                          ^~~~
a.cc:23:26: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:25:9: error: 'cout' was not declared in this scope
   25 |         cout << endl;
      |         ^~~~
a.cc:25:9: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:25:17: error: 'endl' was not declared in this scope
   25 |         cout << endl;
      |                 ^~~~
a.cc:2:1: note: 'std::endl' is defined in header '<ostream>'; this is probably fixable by adding '#include <ostream>'
    1 | #include <stdio.h>
  +++ |+#include <ostream>
    2 | using namespace std;