View Compilation Error

0_0_36869880_16590.cpp:2:11: error: '::main' must return 'int'
 long main()
           ^
0_0_36869880_16590.cpp: In function 'int main()':
0_0_36869880_16590.cpp:5:25: error: 'scanf_s' was not declared in this scope
  while (scanf_s("%d", &a) != EOF)
                         ^