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:11:14: error: lvalue required as left operand of assignment
   11 |   if( x= 'A' || x= 'a'){
      |          ~~~~^~~~
a.cc:14:15: error: lvalue required as left operand of assignment
   14 |    if( x= 'B' || x= 'b'){
      |           ~~~~^~~~
a.cc:17:14: error: lvalue required as left operand of assignment
   17 |   if( x= 'C' || x= 'c'){
      |          ~~~~^~~~
a.cc:20:15: error: lvalue required as left operand of assignment
   20 |    if( x= 'D' || x= 'd'){
      |           ~~~~^~~~
a.cc:23:14: error: lvalue required as left operand of assignment
   23 |   if( x= 'E' || x= 'e'){
      |          ~~~~^~~~
a.cc:26:15: error: lvalue required as left operand of assignment
   26 |    if( x= 'F' || x= 'f'){
      |           ~~~~^~~~
a.cc:29:14: error: lvalue required as left operand of assignment
   29 |   if( x= 'G' || x= 'g'){
      |          ~~~~^~~~
a.cc:32:15: error: lvalue required as left operand of assignment
   32 |    if( x= 'H' || x= 'h'){
      |           ~~~~^~~~
a.cc:35:15: error: lvalue required as left operand of assignment
   35 |    if( x= 'I' || x= 'i'){
      |           ~~~~^~~~
a.cc:38:15: error: lvalue required as left operand of assignment
   38 |    if( x= 'J' || x= 'J'){
      |           ~~~~^~~~
a.cc:41:14: error: lvalue required as left operand of assignment
   41 |   if( x= 'K' || x= 'k'){
      |          ~~~~^~~~
a.cc:44:15: error: lvalue required as left operand of assignment
   44 |    if( x= 'L' || x= 'l'){
      |           ~~~~^~~~
a.cc:47:14: error: lvalue required as left operand of assignment
   47 |   if( x= 'M' || x= 'm'){
      |          ~~~~^~~~
a.cc:50:15: error: lvalue required as left operand of assignment
   50 |    if( x= 'N' || x= 'n'){
      |           ~~~~^~~~
a.cc:53:14: error: lvalue required as left operand of assignment
   53 |   if( x= 'O' || x= 'o'){
      |          ~~~~^~~~
a.cc:56:15: error: lvalue required as left operand of assignment
   56 |    if( x= 'P' || x= 'p'){
      |           ~~~~^~~~
a.cc:59:14: error: lvalue required as left operand of assignment
   59 |   if( x= 'Q' || x= 'q'){
      |          ~~~~^~~~
a.cc:62:15: error: lvalue required as left operand of assignment
   62 |    if( x= 'R' || x= 'r'){
      |           ~~~~^~~~
a.cc:65:14: error: lvalue required as left operand of assignment
   65 |   if( x= 'S' || x= 's'){
      |          ~~~~^~~~
a.cc:68:15: error: lvalue required as left operand of assignment
   68 |    if( x= 'T' || x= 't'){
      |           ~~~~^~~~
a.cc:71:14: error: lvalue required as left operand of assignment
   71 |   if( x= 'U' || x= 'u'){
      |          ~~~~^~~~
a.cc:74:15: error: lvalue required as left operand of assignment
   74 |    if( x= 'V' || x= 'v'){
      |           ~~~~^~~~
a.cc:77:14: error: lvalue required as left operand of assignment
   77 |   if( x= 'W' || x= 'w'){
      |          ~~~~^~~~
a.cc:80:15: error: lvalue required as left operand of assignment
   80 |    if( x= 'X' || x= 'x'){
      |           ~~~~^~~~
a.cc:83:15: error: lvalue required as left operand of assignment
   83 |    if( x= 'Y' || x= 'y'){
      |           ~~~~^~~~
a.cc:86:15: error: lvalue required as left operand of assignment
   86 |    if( x= 'Z' || x= 'z'){
      |           ~~~~^~~~