Language: C++

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

int main() {
  int x;
  cin >> x;

  if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
    cout << A << endl;
  }
  else {
    cout << a << endl;
  }
}


Compiler output:
a.cc: In function 'int main()':
a.cc:8:12: error: 'A' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |            ^
a.cc:8:14: error: 'B' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |              ^
a.cc:8:16: error: 'C' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                ^
a.cc:8:18: error: 'D' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                  ^
a.cc:8:20: error: 'E' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                    ^
a.cc:8:22: error: 'F' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                      ^
a.cc:8:24: error: 'G' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                        ^
a.cc:8:26: error: 'H' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                          ^
a.cc:8:28: error: 'I' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                            ^
a.cc:8:30: error: 'J' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                              ^
a.cc:8:32: error: 'K' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                ^
a.cc:8:34: error: 'L' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                  ^
a.cc:8:36: error: 'N' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                    ^
a.cc:8:38: error: 'M' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                      ^
a.cc:8:40: error: 'O' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                        ^
a.cc:8:42: error: 'P' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                          ^
a.cc:8:44: error: 'Q' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                            ^
a.cc:8:46: error: 'R' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                              ^
a.cc:8:48: error: 'S' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                                ^
a.cc:8:50: error: 'T' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                                  ^
a.cc:8:52: error: 'U' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                                    ^
a.cc:8:54: error: 'V' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                                      ^
a.cc:8:56: error: 'W' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                                        ^
a.cc:8:58: error: 'X' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                                          ^
a.cc:8:60: error: 'Y' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                                            ^
a.cc:8:62: error: 'Z' was not declared in this scope
    8 |   if (x == A,B,C,D,E,F,G,H,I,J,K,L,N,M,O,P,Q,R,S,T,U,V,W,X,Y,Z) {
      |                                                              ^
a.cc:12:13: error: 'a' was not declared in this scope
   12 |     cout << a << endl;
      |             ^