Having some trouble with a challenge problem from my C++ textbook.

The program should take numbers from a text file. It should then display the lowest number in the array, highest number in the array, total sum number of all the numbers in the array, average number of all the numbers in the array

// Function prototypes

double retrieveLowest(double [], double);

double retrieveHighest(double [], double);

double calculateSum(double [], double);

double calculateAverage(double [], double);