foo.cc: In function ‘int main()’:
foo.cc:9:17: error: ‘d’ was not declared in this scope
    9 |                 d=a;
      |                 ^
foo.cc:15:17: error: ‘d’ was not declared in this scope
   15 |                 d=c;
      |                 ^
foo.cc:21:17: error: ‘d’ was not declared in this scope
   21 |                 d=a;
      |                 ^
foo.cc:5:19: warning: unused variable ‘n’ [-Wunused-variable]
    5 |         int a,b,c,n;
      |                   ^