Language: C++

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

int main(){
  vector<string> Letter(3);
  cin >> Letter.at(0) >> Letter.at(1) >> Letter.at(2);

  for(int i = 0; i < 3; i++){
    char x = Letter.at(0).at(0);
  
  if( x='A' || x='a'){
    cout << "A" << endl;
  }
   if( x='B' || x='b'){
    cout << "B" << endl;
  }
  if( x='C' || x='c'){
    cout << "C" << endl;
  }
   if( x='D' || x='d'){
    cout << "D" << endl;
  }  
  if( x='E' || x='e'){
    cout << "E" << endl;
  }
   if( x='F' || x='f'){
    cout << "F" << endl;
  }
  if( x='G' || x='g'){
    cout << "G" << endl;
  }
   if( x='H' || x='h'){
    cout << "H" << endl;
  }  
   if( x='I' || x='i'){
    cout << "I" << endl;
  }
   if( x='J' || x='J'){
    cout << "J" << endl;
  }
  if( x='K' || x='k'){
    cout << "K" << endl;
  }
   if( x='L' || x='l'){
    cout << "L" << endl;
  }  
  if( x='M' || x='m'){
    cout << "M" << endl;
  }
   if( x='N' || x='n'){
    cout << "N" << endl;
  }
  if( x='O' || x='o'){
    cout << "O" << endl;
  }
   if( x='P' || x='p'){
    cout << "P" << endl;
  }    
  if( x='Q' || x='q'){
    cout << "Q" << endl;
  }
   if( x='R' || x='r'){
    cout << "R" << endl;
  }
  if( x='S' || x='s'){
    cout << "S" << endl;
  }
   if( x='T' || x='t'){
    cout << "T" << endl;
  }  
  if( x='U' || x='u'){
    cout << "U" << endl;
  }
   if( x='V' || x='v'){
    cout << "V" << endl;
  }
  if( x='W' || x='w'){
    cout << "W" << endl;
  }
   if( x='X' || x='x'){
    cout << "X" << endl;
  }  
   if( x='Y' || x='y'){
    cout << "Y" << endl;
  }
   if( x='Z' || x='z'){
    cout << "Z" << endl;
  }
  }
}
 
  
  


Compiler output:
a.cc: In function 'int main()':
a.cc:11:13: error: lvalue required as left operand of assignment
   11 |   if( x='A' || x='a'){
      |         ~~~~^~~~
a.cc:14:14: error: lvalue required as left operand of assignment
   14 |    if( x='B' || x='b'){
      |          ~~~~^~~~
a.cc:17:13: error: lvalue required as left operand of assignment
   17 |   if( x='C' || x='c'){
      |         ~~~~^~~~
a.cc:20:14: error: lvalue required as left operand of assignment
   20 |    if( x='D' || x='d'){
      |          ~~~~^~~~
a.cc:23:13: error: lvalue required as left operand of assignment
   23 |   if( x='E' || x='e'){
      |         ~~~~^~~~
a.cc:26:14: error: lvalue required as left operand of assignment
   26 |    if( x='F' || x='f'){
      |          ~~~~^~~~
a.cc:29:13: error: lvalue required as left operand of assignment
   29 |   if( x='G' || x='g'){
      |         ~~~~^~~~
a.cc:32:14: error: lvalue required as left operand of assignment
   32 |    if( x='H' || x='h'){
      |          ~~~~^~~~
a.cc:35:14: error: lvalue required as left operand of assignment
   35 |    if( x='I' || x='i'){
      |          ~~~~^~~~
a.cc:38:14: error: lvalue required as left operand of assignment
   38 |    if( x='J' || x='J'){
      |          ~~~~^~~~
a.cc:41:13: error: lvalue required as left operand of assignment
   41 |   if( x='K' || x='k'){
      |         ~~~~^~~~
a.cc:44:14: error: lvalue required as left operand of assignment
   44 |    if( x='L' || x='l'){
      |          ~~~~^~~~
a.cc:47:13: error: lvalue required as left operand of assignment
   47 |   if( x='M' || x='m'){
      |         ~~~~^~~~
a.cc:50:14: error: lvalue required as left operand of assignment
   50 |    if( x='N' || x='n'){
      |          ~~~~^~~~
a.cc:53:13: error: lvalue required as left operand of assignment
   53 |   if( x='O' || x='o'){
      |         ~~~~^~~~
a.cc:56:14: error: lvalue required as left operand of assignment
   56 |    if( x='P' || x='p'){
      |          ~~~~^~~~
a.cc:59:13: error: lvalue required as left operand of assignment
   59 |   if( x='Q' || x='q'){
      |         ~~~~^~~~
a.cc:62:14: error: lvalue required as left operand of assignment
   62 |    if( x='R' || x='r'){
      |          ~~~~^~~~
a.cc:65:13: error: lvalue required as left operand of assignment
   65 |   if( x='S' || x='s'){
      |         ~~~~^~~~
a.cc:68:14: error: lvalue required as left operand of assignment
   68 |    if( x='T' || x='t'){
      |          ~~~~^~~~
a.cc:71:13: error: lvalue required as left operand of assignment
   71 |   if( x='U' || x='u'){
      |         ~~~~^~~~
a.cc:74:14: error: lvalue required as left operand of assignment
   74 |    if( x='V' || x='v'){
      |          ~~~~^~~~
a.cc:77:13: error: lvalue required as left operand of assignment
   77 |   if( x='W' || x='w'){
      |         ~~~~^~~~
a.cc:80:14: error: lvalue required as left operand of assignment
   80 |    if( x='X' || x='x'){
      |          ~~~~^~~~
a.cc:83:14: error: lvalue required as left operand of assignment
   83 |    if( x='Y' || x='y'){
      |          ~~~~^~~~
a.cc:86:14: error: lvalue required as left operand of assignment
   86 |    if( x='Z' || x='z'){
      |          ~~~~^~~~