Language: C++

#include <stdio.h>
using namespace std;

int main() {
	string st;
	string w[3]={"the","this","that"};
	int wn[3]={3,4,4},k,i,j,s,f;
	while(getline(cin,st)) {
    k=0;
	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;
		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')) ; else cout << st[i];
	}	
	cout << endl;
	}
    return 0;
	}

Compiler output:
a.cc: In function 'int main()':
a.cc:5:9: error: 'string' was not declared in this scope
    5 |         string 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:6:15: error: expected ';' before 'w'
    6 |         string w[3]={"the","this","that"};
      |               ^~
      |               ;
a.cc:8:23: error: 'cin' was not declared in this scope
    8 |         while(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:8:27: error: 'st' was not declared in this scope; did you mean 's'?
    8 |         while(getline(cin,st)) {
      |                           ^~
      |                           s
a.cc:14:54: error: 'w' was not declared in this scope
   14 |                         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:21:67: error: 'cout' was not declared in this scope
   21 |         for (i=0;i<st.size();i++) if ((st[i]>='a' && st[i]<='z')) cout << (char)(st[i]-(st[k]-'t')) ; else cout << st[i];
      |                                                                   ^~~~
a.cc:21:67: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:21:108: error: 'cout' was not declared in this scope
   21 |         for (i=0;i<st.size();i++) if ((st[i]>='a' && st[i]<='z')) cout << (char)(st[i]-(st[k]-'t')) ; else cout << st[i];
      |                                                                                                            ^~~~
a.cc:21:108: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:23:9: error: 'cout' was not declared in this scope
   23 |         cout << endl;
      |         ^~~~
a.cc:23:9: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:23:17: error: 'endl' was not declared in this scope
   23 |         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;