View Compilation Error

0_0_33139095_306.cpp: In function 'int main()':
0_0_33139095_306.cpp:17:30: error: 'scanf_s' was not declared in this scope
    scanf_s("%s", a, sizeof(a));
                              ^
0_0_33139095_306.cpp:18:21: error: 'strlen' was not declared in this scope
    ll len = strlen(a);
                     ^