/in/foo.cc: In function 'int main()':
/in/foo.cc:10:3: error: 'd' was not declared in this scope
   10 |   d=(b-a)/c;
      |   ^
/in/foo.cc:7:6: warning: unused variable 'n' [-Wunused-variable]
    7 |  int n;
      |      ^