foo.cc: In function ‘int main()’:
foo.cc:7:21: warning: format ‘%lf’ expects argument of type ‘double’, but argument 2 has type ‘int’ [-Wformat=]
    7 |         printf("%.9lf",a/b);
      |                 ~~~~^  ~~~
      |                     |   |
      |                     |   int
      |                     double
      |                 %.9d