/in/foo.cc: In function 'int main()':
/in/foo.cc:7:28: warning: right operand of comma operator has no effect [-Wunused-value]
  for(int i=1;i<=n;i++,b++,n-i)
                           ~^~
/in/foo.cc:9:25: warning: right operand of comma operator has no effect [-Wunused-value]
   for(int i=1;i<=b;i++,b-i)
                        ~^~
/in/foo.cc:5:8: warning: unused variable 'a' [-Wunused-variable]
  int n,a,b,k=0;
        ^
/in/foo.cc:14:1: error: expected '}' at end of input
 }
 ^