foo.c:2:1: error: unknown type name 'using'
    2 | using namespace std;
      | ^~~~~
foo.c:2:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
    2 | using namespace std;
      |                 ^~~
foo.c: In function 'main':
foo.c:8:9: error: 'cin' undeclared (first use in this function)
    8 |         cin>>n
      |         ^~~
foo.c:8:9: note: each undeclared identifier is reported only once for each function it appears in
foo.c:8:15: error: expected ';' before 'a'
    8 |         cin>>n
      |               ^
      |               ;
    9 |         a[1]=1
      |         ~      
foo.c:17:25: warning: missing terminating " character
   17 |                 cout << "2” << end1；
      |                         ^
foo.c:17:25: error: missing terminating " character
   17 |                 cout << "2” << end1；
      |                         ^~~~~~~~~~~~~
foo.c:7:13: warning: unused variable 'i' [-Wunused-variable]
    7 |         int i,n;
      |             ^
foo.c:6:25: warning: unused variable 's' [-Wunused-variable]
    6 |         long long a[50],s=0;
      |                         ^
foo.c:6:19: warning: unused variable 'a' [-Wunused-variable]
    6 |         long long a[50],s=0;
      |                   ^

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