Language: C++

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

int main() {
  string A; string B; string C;
  cin>>A>>B>>C;
  char a; char b; char c;   char d; char e; char f; char g; char h; char i;
  char j ;char k; char l; char m; char n;  char o; char p; char q; char r; char s; char t; char u; char v; char w; char x; char y; char z;
  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:9:5: error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'char' in assignment
    9 |   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;
      |     ^
      |     |
      |     std::string {aka std::__cxx11::basic_string<char>}
a.cc:9:10: error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'char' in assignment
    9 |   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;
      |          ^
      |          |
      |          std::string {aka std::__cxx11::basic_string<char>}
a.cc:9:15: error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'char' in assignment
    9 |   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;
      |               ^
      |               |
      |               std::string {aka std::__cxx11::basic_string<char>}
a.cc:9:20: error: 'D' was not declared in this scope
    9 |   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:9:25: error: 'E' was not declared in this scope
    9 |   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:9:30: error: 'F' was not declared in this scope
    9 |   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:9:35: error: 'G' was not declared in this scope
    9 |   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:9:40: error: 'H' was not declared in this scope
    9 |   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:9:45: error: 'I' was not declared in this scope
    9 |   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:9:50: error: 'J' was not declared in this scope
    9 |   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:9:55: error: 'K' was not declared in this scope
    9 |   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:9:60: error: 'L' was not declared in this scope
    9 |   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:9:65: error: 'M' was not declared in this scope
    9 |   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:9:70: error: 'N' was not declared in this scope
    9 |   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:10:5: error: 'O' was not declared in this scope
   10 |   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:10:10: error: 'P' was not declared in this scope
   10 |   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:10:15: error: 'Q' was not declared in this scope
   10 |   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:10:20: error: 'R' was not declared in this scope
   10 |   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:10:25: error: 'S' was not declared in this scope
   10 |   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:10:30: error: 'T' was not declared in this scope
   10 |   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:10:35: error: 'U' was not declared in this scope
   10 |   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:10:40: error: 'V' was not declared in this scope
   10 |   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:10:45: error: 'W' was not declared in this scope
   10 |   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:10:50: error: 'X' was not declared in this scope
   10 |   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:10:55: error: 'Y' was not declared in this scope
   10 |   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:10:60: error: 'Z' was not declared in this scope
   10 |   o=O; p=P; q=Q; r=R; s=S; t=T; u=U; v=V; w=W; x=X; y=Y; z=Z;
      |                                                            ^