/in/foo.cc: In function 'int main()':
/in/foo.cc:5:18: error: expected initializer before '.' token
    5 |         int a,b,c.n;
      |                  ^
/in/foo.cc:7:25: error: 'n' was not declared in this scope
    7 |         for (int i=1;i<=n;i++)
      |                         ^
/in/foo.cc:9:17: error: 'c' was not declared in this scope
    9 |                 c=b+(b-a);
      |                 ^
/in/foo.cc:13:15: error: 'c' was not declared in this scope
   13 |         cout<<c;
      |               ^