foo.cc: In function 'int main()':
foo.cc:19:17: error: 'cout' was not declared in this scope
   19 |                 cout<<"请输入要验证的偶数(该数>=6)：";
      |                 ^~~~
foo.cc:3:1: note: 'std::cout' is defined in header '<iostream>'; did you forget to '#include <iostream>'?
    2 | #include<cmath>
  +++ |+#include <iostream>
    3 | using namespace std;
foo.cc:20:17: error: 'cin' was not declared in this scope
   20 |                 cin>>a;
      |                 ^~~
foo.cc:20:17: note: 'std::cin' is defined in header '<iostream>'; did you forget to '#include <iostream>'?
foo.cc:45:55: error: 'endl' was not declared in this scope
   45 |                                                 cout<<endl;//每4个换行
      |                                                       ^~~~
foo.cc:3:1: note: 'std::endl' is defined in header '<ostream>'; did you forget to '#include <ostream>'?
    2 | #include<cmath>
  +++ |+#include <ostream>
    3 | using namespace std;
foo.cc: In function 'bool shushu(int)':
foo.cc:15:1: warning: control reaches end of non-void function [-Wreturn-type]
   15 | } //判断质数的函数
      | ^

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