foo.cc: In function ‘int main()’:
foo.cc:6:9: error: ‘cin’ was not declared in this scope
    6 |         cin>>b1>>a1>>b2>>a2;
      |         ^~~
foo.cc:2:1: note: ‘std::cin’ is defined in header ‘<iostream>’; did you forget to ‘#include <iostream>’?
    1 | #include <stdio.h>
  +++ |+#include <iostream>
    2 | using namespace std;
foo.cc:19:13: error: ‘cout’ was not declared in this scope
   19 |             cout<<fenzi/j<<" "<<fenmu/j;
      |             ^~~~
foo.cc:19:13: note: ‘std::cout’ is defined in header ‘<iostream>’; did you forget to ‘#include <iostream>’?