View Compilation Error

2_29342_2308290_8741.cpp: In function 'int main()':
2_29342_2308290_8741.cpp:40:18: error: 'scanf_s' was not declared in this scope
  scanf_s("%d", &n);
                  ^
2_29342_2308290_8741.cpp:54:17: error: 'strlen' was not declared in this scope
   if(strlen(str1)==0&&strlen(str1)==0)
                 ^
2_29342_2308290_8741.cpp:59:17: error: 'strlen' was not declared in this scope
   if(strlen(str1)==0)
                 ^
2_29342_2308290_8741.cpp:64:17: error: 'strlen' was not declared in this scope
   if(strlen(str2)==0)
                 ^
2_29342_2308290_8741.cpp:70:17: error: 'strlen' was not declared in this scope
   if(strlen(str1)==strlen(str2))
                 ^