View Compilation Error

0_0_15220796_18811.cpp:2:11: error: '::main' must return 'int'
 void main()
           ^
0_0_15220796_18811.cpp: In function 'int main()':
0_0_15220796_18811.cpp:5:46: error: 'scanf_s' was not declared in this scope
  while (scanf_s("%d %d %d %d", &a, &b, &s, &t) && a)
                                              ^