Language: C++

#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)


int main() {
  long long N;
  cin >> N;
  
  long long x=N;
  int y;
  vector<int> vec;
  
  for (int i = 0; i < 100; i++){
    x = x/26;
    y = N%26;
    
    vec.at(i) =y;
    
    if(x==0){
      break;
    }
  }
  
  reverse(vec.begin(), vec.end());
  string S;
  
  for(int i = 0; i<100; i++){
    if(vec.at(i) ==1){
      S.at(i)="a";
    }
    else if(vec.at(i) ==2){
      S.at(i)="b";
    }
    else if(vec.at(i) ==3){
      S.at(i)="c";
    }
    else if(vec.at(i) ==4){
      S.at(i)="d";
    }
    else if(vec.at(i) ==5){
      S.at(i)="e";
    }
    else if(vec.at(i) ==6){
      S.at(i)="f";
    }
    else if(vec.at(i) ==7){
      S.at(i)="g";
    }
    else if(vec.at(i) ==8){
      S.at(i)="h";
    }
    else if(vec.at(i) ==9){
      S.at(i)="i";
    }
    else if(vec.at(i) ==10){
      S.at(i)="j";
    }
    else if(vec.at(i) ==11){
      S.at(i)="k";
    }
    else if(vec.at(i) ==12){
      S.at(i)="l";
    }
    else if(vec.at(i) ==13){
      S.at(i)="m";
    }
    else if(vec.at(i) ==14){
      S.at(i)="n";
    }
    else if(vec.at(i) ==15){
      S.at(i)="o";
    }
    else if(vec.at(i) ==16){
      S.at(i)="p";
    }
    else if(vec.at(i) ==17){
      S.at(i)="q";
    }
    else if(vec.at(i) ==18){
      S.at(i)="r";
    }
    else if(vec.at(i) ==19){
      S.at(i)="s";
    }
    else if(vec.at(i) ==20){
      S.at(i)="t";
    }
    else if(vec.at(i) ==21){
      S.at(i)="u";
    }
    else if(vec.at(i) ==22){
      S.at(i)="v";
    }
    else if(vec.at(i) ==23){
      S.at(i)="w";
    }
    else if(vec.at(i) ==24){
      S.at(i)="x";
    }
    else if(vec.at(i) ==25){
      S.at(i)="y";
    }
    else if(vec.at(i) ==26){
      S.at(i)="z";
    }
    else{
      break;
    }
    
  cout << S.at(i);
  }
}


Compiler output:
a.cc: In function 'int main()':
a.cc:30:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   30 |       S.at(i)="a";
      |               ^~~
      |               |
      |               const char*
a.cc:33:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   33 |       S.at(i)="b";
      |               ^~~
      |               |
      |               const char*
a.cc:36:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   36 |       S.at(i)="c";
      |               ^~~
      |               |
      |               const char*
a.cc:39:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   39 |       S.at(i)="d";
      |               ^~~
      |               |
      |               const char*
a.cc:42:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   42 |       S.at(i)="e";
      |               ^~~
      |               |
      |               const char*
a.cc:45:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   45 |       S.at(i)="f";
      |               ^~~
      |               |
      |               const char*
a.cc:48:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   48 |       S.at(i)="g";
      |               ^~~
      |               |
      |               const char*
a.cc:51:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   51 |       S.at(i)="h";
      |               ^~~
      |               |
      |               const char*
a.cc:54:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   54 |       S.at(i)="i";
      |               ^~~
      |               |
      |               const char*
a.cc:57:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   57 |       S.at(i)="j";
      |               ^~~
      |               |
      |               const char*
a.cc:60:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   60 |       S.at(i)="k";
      |               ^~~
      |               |
      |               const char*
a.cc:63:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   63 |       S.at(i)="l";
      |               ^~~
      |               |
      |               const char*
a.cc:66:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   66 |       S.at(i)="m";
      |               ^~~
      |               |
      |               const char*
a.cc:69:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   69 |       S.at(i)="n";
      |               ^~~
      |               |
      |               const char*
a.cc:72:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   72 |       S.at(i)="o";
      |               ^~~
      |               |
      |               const char*
a.cc:75:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   75 |       S.at(i)="p";
      |               ^~~
      |               |
      |               const char*
a.cc:78:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   78 |       S.at(i)="q";
      |               ^~~
      |               |
      |               const char*
a.cc:81:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   81 |       S.at(i)="r";
      |               ^~~
      |               |
      |               const char*
a.cc:84:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   84 |       S.at(i)="s";
      |               ^~~
      |               |
      |               const char*
a.cc:87:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   87 |       S.at(i)="t";
      |               ^~~
      |               |
      |               const char*
a.cc:90:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   90 |       S.at(i)="u";
      |               ^~~
      |               |
      |               const char*
a.cc:93:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   93 |       S.at(i)="v";
      |               ^~~
      |               |
      |               const char*
a.cc:96:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   96 |       S.at(i)="w";
      |               ^~~
      |               |
      |               const char*
a.cc:99:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
   99 |       S.at(i)="x";
      |               ^~~
      |               |
      |               const char*
a.cc:102:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
  102 |       S.at(i)="y";
      |               ^~~
      |               |
      |               const char*
a.cc:105:15: error: invalid conversion from 'const char*' to '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} [-fpermissive]
  105 |       S.at(i)="z";
      |               ^~~
      |               |
      |               const char*