Language: C++

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

int main() {
  string A; string B; string C;
  cin>>A>>B>>C;
  a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
  o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
  cout<<A.at(0)<<B.at(0)<<C.at(0)<<endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:7:3: error: 'a' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |   ^
a.cc:7:8: error: 'b' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |        ^
a.cc:7:13: error: 'c' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |             ^
a.cc:7:18: error: 'd' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                  ^
a.cc:7:20: error: 'D' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                    ^
a.cc:7:23: error: 'e' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                       ^
a.cc:7:25: error: 'E' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                         ^
a.cc:7:28: error: 'f' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                            ^
a.cc:7:30: error: 'F' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                              ^
a.cc:7:33: error: 'g' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                 ^
a.cc:7:35: error: 'G' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                   ^
a.cc:7:38: error: 'h' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                      ^
a.cc:7:40: error: 'H' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                        ^
a.cc:7:43: error: 'i' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                           ^
a.cc:7:45: error: 'I' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                             ^
a.cc:7:48: error: 'j' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                                ^
a.cc:7:50: error: 'J' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                                  ^
a.cc:7:53: error: 'k' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                                     ^
a.cc:7:55: error: 'K' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                                       ^
a.cc:7:58: error: 'l' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                                          ^
a.cc:7:60: error: 'L' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                                            ^
a.cc:7:63: error: 'm' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                                               ^
a.cc:7:65: error: 'M' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                                                 ^
a.cc:7:68: error: 'n' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                                                    ^
a.cc:7:70: error: 'N' was not declared in this scope
    7 |   a=A; b=B; c=C; d=D; e=E; f=F; g=G; h=H; i=I; j=J; k=K; l=L; m=M; n=N;
      |                                                                      ^
a.cc:8:3: error: 'o' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |   ^
a.cc:8:5: error: 'O' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |     ^
a.cc:8:8: error: 'p' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |        ^
a.cc:8:10: error: 'P' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |          ^
a.cc:8:13: error: 'q' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |             ^
a.cc:8:15: error: 'Q' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |               ^
a.cc:8:18: error: 'r' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                  ^
a.cc:8:20: error: 'R' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                    ^
a.cc:8:23: error: 's' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                       ^
a.cc:8:25: error: 'S' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                         ^
a.cc:8:28: error: 't' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                            ^
a.cc:8:30: error: 'T' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                              ^
a.cc:8:33: error: 'u' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                 ^
a.cc:8:35: error: 'U' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                   ^
a.cc:8:38: error: 'v' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                      ^
a.cc:8:40: error: 'V' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                        ^
a.cc:8:43: error: 'w' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                           ^
a.cc:8:45: error: 'W' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                             ^
a.cc:8:48: error: 'x' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                                ^
a.cc:8:50: error: 'X' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                                  ^
a.cc:8:53: error: 'y' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                                     ^
a.cc:8:55: error: 'Y' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                                       ^
a.cc:8:58: error: 'z' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                                          ^
a.cc:8:60: error: 'Z' was not declared in this scope
    8 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                                            ^