View Compilation Error

0_0_39457737_16955.c:2:1: error: unknown type name 'using'
    2 | using namespace std;
      | ^~~~~
0_0_39457737_16955.c:2:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
    2 | using namespace std;
      |                 ^~~
0_0_39457737_16955.c: In function 'solve':
0_0_39457737_16955.c:21:9: error: 'cin' undeclared (first use in this function)
   21 |         cin >> a >> b;
      |         ^~~
0_0_39457737_16955.c:21:9: note: each undeclared identifier is reported only once for each function it appears in
0_0_39457737_16955.c:22:9: error: 'cout' undeclared (first use in this function)
   22 |         cout << a * inv(b) % mod << '\n';
      |         ^~~~
0_0_39457737_16955.c: In function 'main':
0_0_39457737_16955.c:26:9: error: 'cin' undeclared (first use in this function)
   26 |         cin >> t;
      |         ^~~