/in/foo.cc:2:7: error: expected nested-name-specifier before 'namespac'
 using namespac std;
       ^~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:10:25: warning: too many arguments for format [-Wformat-extra-args]
     printf("%.4lf",a,b,c);
                         ^