Have issues determining if array is sorted - c++

Question

I trying to figure out if an array set is sorted or not using sentinal-terminated sequences.
In attempting I have tried to check if the array is ascending, descending, or not sorted.
#define isNaN(X) (X != X)
#define NaN std::numeric_limits<float>::quiet_NaN()
enum sortType { ASCENDING, DESCENDING, UNKNOWN, UNSORTED };
I think there is an error in my bool inSorted function and I believe the issue is with for checking the NaN value at the end.
bool isSorted(const float data[], const int currentDataItem, const sortType typeOfSort) {
switch(typeOfSort) {
case ASCENDING:
if(currentDataItem == 0){
return isSorted(data, (currentDataItem + 1), ASCENDING);
} else if(data[currentDataItem] > data[currentDataItem+1]){
return false;
} else if(data[currentDataItem] == data[currentDataItem]){
return isSorted(data, (currentDataItem+1), ASCENDING);
} else {
return true;
}
case DESCENDING:
if(currentDataItem == 0){
return isSorted(data, (currentDataItem + 1), DESCENDING);
} else if(data[currentDataItem] < data[currentDataItem+1]){
return false;
} else if(data[currentDataItem] == data[currentDataItem]){
return isSorted(data, (currentDataItem+1), DESCENDING);
} else {
return true;
}
}
}
The isSorted is then called by bool sorted
bool sorted(const float data[]) {
bool ascending = isSorted(data, 0, ASCENDING);
bool descending = isSorted(data, 0, DESCENDING);
if(!ascending && !descending){
return false;
}
return true;
}
Wrapped up by main
int main(const int argc, const char* const argv[]) {
float data[] = {1, 2, 4, 5, 6, NaN};
if (sorted(data))
cout << "Data is sorted" << endl;
else
cout << "Data is not sorted" << endl;
return 0;
}

Answer 1

When implementing a recursive function, you need to ask yourself the following questions explicitly:
What is the base case of your recursive function?
What is the recursive case of your recursive function?
Answers:
If the current array position compares against NaN, then we are sorted.
If our position is not sorted, we know the list isn't sorted. If our position is sorted, then the array is sorted if the recursive condition holds on the next pair.
Therefore:
case ASCENDING:
// Empty list
if (std::isnan(data[currentDataItem]))
return true;
// One element list.
else if (std::isnan(data[currentDataItem + 1])
return true;
// Recursive case: we've found a location where the data isn't sorted.
else if (data[currentDataItem] > data[currentDataItem + 1])
return false;
// This location is sorted, check the next location.
else
return isSorted(data, currentDataItem + 1, typeOfSort);
Note that I only directly return true; on the base cases. Otherwise, we either fail the function, or we recurse.