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


Compiler output:
a.cc: In function 'int main()':
a.cc:11:15: error: lvalue required as left operand of assignment
   11 |   if( x = 'A' || x = 'a'){
      |           ~~~~^~~~
a.cc:14:16: error: lvalue required as left operand of assignment
   14 |    if( x = 'B' || x = 'b'){
      |            ~~~~^~~~
a.cc:17:15: error: lvalue required as left operand of assignment
   17 |   if( x = 'C' || x = 'c'){
      |           ~~~~^~~~
a.cc:20:16: error: lvalue required as left operand of assignment
   20 |    if( x = 'D' || x = 'd'){
      |            ~~~~^~~~
a.cc:23:15: error: lvalue required as left operand of assignment
   23 |   if( x = 'E' || x = 'e'){
      |           ~~~~^~~~
a.cc:26:16: error: lvalue required as left operand of assignment
   26 |    if( x = 'F' || x = 'f'){
      |            ~~~~^~~~
a.cc:29:15: error: lvalue required as left operand of assignment
   29 |   if( x = 'G' || x = 'g'){
      |           ~~~~^~~~
a.cc:32:16: error: lvalue required as left operand of assignment
   32 |    if( x = 'H' || x = 'h'){
      |            ~~~~^~~~
a.cc:35:16: error: lvalue required as left operand of assignment
   35 |    if( x = 'I' || x = 'i'){
      |            ~~~~^~~~
a.cc:38:16: error: lvalue required as left operand of assignment
   38 |    if( x = 'J' || x = 'J'){
      |            ~~~~^~~~
a.cc:41:15: error: lvalue required as left operand of assignment
   41 |   if( x = 'K' || x = 'k'){
      |           ~~~~^~~~
a.cc:44:16: error: lvalue required as left operand of assignment
   44 |    if( x = 'L' || x = 'l'){
      |            ~~~~^~~~
a.cc:47:15: error: lvalue required as left operand of assignment
   47 |   if( x = 'M' || x = 'm'){
      |           ~~~~^~~~
a.cc:50:16: error: lvalue required as left operand of assignment
   50 |    if( x = 'N' || x = 'n'){
      |            ~~~~^~~~
a.cc:53:15: error: lvalue required as left operand of assignment
   53 |   if( x = 'O' || x = 'o'){
      |           ~~~~^~~~
a.cc:56:16: error: lvalue required as left operand of assignment
   56 |    if( x = 'P' || x = 'p'){
      |            ~~~~^~~~
a.cc:59:15: error: lvalue required as left operand of assignment
   59 |   if( x = 'Q' || x = 'q'){
      |           ~~~~^~~~
a.cc:62:16: error: lvalue required as left operand of assignment
   62 |    if( x = 'R' || x = 'r'){
      |            ~~~~^~~~
a.cc:65:15: error: lvalue required as left operand of assignment
   65 |   if( x = 'S' || x = 's'){
      |           ~~~~^~~~
a.cc:68:16: error: lvalue required as left operand of assignment
   68 |    if( x = 'T' || x = 't'){
      |            ~~~~^~~~
a.cc:71:15: error: lvalue required as left operand of assignment
   71 |   if( x = 'U' || x = 'u'){
      |           ~~~~^~~~
a.cc:74:16: error: lvalue required as left operand of assignment
   74 |    if( x = 'V' || x = 'v'){
      |            ~~~~^~~~
a.cc:77:15: error: lvalue required as left operand of assignment
   77 |   if( x = 'W' || x = 'w'){
      |           ~~~~^~~~
a.cc:80:16: error: lvalue required as left operand of assignment
   80 |    if( x = 'X' || x = 'x'){
      |            ~~~~^~~~
a.cc:83:16: error: lvalue required as left operand of assignment
   83 |    if( x = 'Y' || x = 'y'){
      |            ~~~~^~~~
a.cc:86:16: error: lvalue required as left operand of assignment
   86 |    if( x = 'Z' || x = 'z'){
      |            ~~~~^~~~