Language: C++

#include<bits/stdc++.h>
using namespace std;

int main()
{
  string S;
  int N,length;
  cin>>N>>S;
  length=S.size();
  for(int i=0;i<N;i++){
    for(int j=0;j<length;j++){
      if(S[j]=="A")S[j]="B";
      else if(S[j]=="B")S[j]="C";
      else if(S[j]=="C")S[j]="D";
      else if(S[j]=="D")S[j]="E";
      else if(S[j]=="E")S[j]="F";
      else if(S[j]=="F")S[j]="G";
      else if(S[j]=="G")S[j]="H";
      else if(S[j]=="H")S[j]="I";
      else if(S[j]=="I")S[j]="J";
      else if(S[j]=="J")S[j]="K";
      else if(S[j]=="K")S[j]="L";
      else if(S[j]=="L")S[j]="M";
      else if(S[j]=="M")S[j]="N";
      else if(S[j]=="N")S[j]="O";
      else if(S[j]=="O")S[j]="P";
      else if(S[j]=="P")S[j]="Q";
      else if(S[j]=="Q")S[j]="R";
      else if(S[j]=="R")S[j]="S";
      else if(S[j]=="S")S[j]="T";
      else if(S[j]=="T")S[j]="U";
      else if(S[j]=="U")S[j]="V";
      else if(S[j]=="V")S[j]="W";
      else if(S[j]=="W")S[j]="X";
      else if(S[j]=="X")S[j]="Y";
      else if(S[j]=="Y")S[j]="Z";
      else if(S[j]=="Z")S[j]="A";
    }
  }
  cout<<S<<endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:12:14: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   12 |       if(S[j]=="A")S[j]="B";
a.cc:12:25: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   12 |       if(S[j]=="A")S[j]="B";
      |                         ^~~
      |                         |
      |                         const char*
a.cc:13:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   13 |       else if(S[j]=="B")S[j]="C";
a.cc:13:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   13 |       else if(S[j]=="B")S[j]="C";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:14:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   14 |       else if(S[j]=="C")S[j]="D";
a.cc:14:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   14 |       else if(S[j]=="C")S[j]="D";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:15:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   15 |       else if(S[j]=="D")S[j]="E";
a.cc:15:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   15 |       else if(S[j]=="D")S[j]="E";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:16:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   16 |       else if(S[j]=="E")S[j]="F";
a.cc:16:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   16 |       else if(S[j]=="E")S[j]="F";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:17:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   17 |       else if(S[j]=="F")S[j]="G";
a.cc:17:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   17 |       else if(S[j]=="F")S[j]="G";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:18:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   18 |       else if(S[j]=="G")S[j]="H";
a.cc:18:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   18 |       else if(S[j]=="G")S[j]="H";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:19:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   19 |       else if(S[j]=="H")S[j]="I";
a.cc:19:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   19 |       else if(S[j]=="H")S[j]="I";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:20:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   20 |       else if(S[j]=="I")S[j]="J";
a.cc:20:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   20 |       else if(S[j]=="I")S[j]="J";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:21:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   21 |       else if(S[j]=="J")S[j]="K";
a.cc:21:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   21 |       else if(S[j]=="J")S[j]="K";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:22:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   22 |       else if(S[j]=="K")S[j]="L";
a.cc:22:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   22 |       else if(S[j]=="K")S[j]="L";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:23:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   23 |       else if(S[j]=="L")S[j]="M";
a.cc:23:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   23 |       else if(S[j]=="L")S[j]="M";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:24:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   24 |       else if(S[j]=="M")S[j]="N";
a.cc:24:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   24 |       else if(S[j]=="M")S[j]="N";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:25:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   25 |       else if(S[j]=="N")S[j]="O";
a.cc:25:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   25 |       else if(S[j]=="N")S[j]="O";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:26:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   26 |       else if(S[j]=="O")S[j]="P";
a.cc:26:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   26 |       else if(S[j]=="O")S[j]="P";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:27:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   27 |       else if(S[j]=="P")S[j]="Q";
a.cc:27:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   27 |       else if(S[j]=="P")S[j]="Q";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:28:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   28 |       else if(S[j]=="Q")S[j]="R";
a.cc:28:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   28 |       else if(S[j]=="Q")S[j]="R";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:29:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   29 |       else if(S[j]=="R")S[j]="S";
a.cc:29:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   29 |       else if(S[j]=="R")S[j]="S";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:30:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   30 |       else if(S[j]=="S")S[j]="T";
a.cc:30:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   30 |       else if(S[j]=="S")S[j]="T";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:31:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   31 |       else if(S[j]=="T")S[j]="U";
a.cc:31:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   31 |       else if(S[j]=="T")S[j]="U";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:32:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   32 |       else if(S[j]=="U")S[j]="V";
a.cc:32:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   32 |       else if(S[j]=="U")S[j]="V";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:33:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   33 |       else if(S[j]=="V")S[j]="W";
a.cc:33:30: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   33 |       else if(S[j]=="V")S[j]="W";
      |                              ^~~
      |                              |
      |                              const char*
a.cc:34:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   34 |       else if(S[j]=="W")S[j]="X";
a.cc:34:30: error: invalid