foo.cc:59:10: error: 'istream' does not name a type
   59 |   friend istream &operator >>(istream &in, matrix &m) {
      |          ^~~~~~~
foo.cc:67:10: error: 'ostream' does not name a type
   67 |   friend ostream &operator <<(ostream &out, matrix &m) {
      |          ^~~~~~~
foo.cc: In function 'int main()':
foo.cc:80:2: error: 'cin' was not declared in this scope
   80 |  cin >> k;
      |  ^~~
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:86:2: error: 'cout' was not declared in this scope
   86 |  cout << ans1 << ans2;
      |  ^~~~
foo.cc:86:2: note: 'std::cout' is defined in header '<iostream>'; did you forget to '#include <iostream>'?

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