Day6 Pull Request for Code Review

For Lines175 ~187, I think we can minimize the usage of the for-loops to once, by just indicating which "size" is to be used by category. Example:
```
int categorySize = 0;
if (choices==categoryEasy) {
    categorySize = easySize;
} else if ...
``` Then just assign the categorySize to the for-loop like this:
```
for (int i = 0; i < categorySize; i++)  {
....
``` :bow: