string? readResult;
int startIndex = 0;
bool goodEntry = false;

int[] numbers = { 1, 2, 3, 4, 5 };

// Display the array to the console.
Console.Clear();
Console.Write("\n\rThe 'numbers' array contains: { ");
foreach (int number in numbers) {
    Console.Write($"{number} ");
}

// To calculate a sum of array elements, 
//  prompt the user for the starting element number.
Console.WriteLine($"}}\n\r\n\rTo sum values 'n' through 5, enter a value for 'n':");
while (goodEntry == false) {
    readResult = Console.ReadLine();
    goodEntry = int.TryParse(readResult, out startIndex);
    if (startIndex > 5) {
        goodEntry = false;
        Console.WriteLine("\n\rEnter an integer value between 1 and 5");
    }
}

// Display the sum and then pause.
Console.WriteLine(
    $"\n\rThe sum of numbers {startIndex} through " +
    $"{numbers.Length} is: {SumValues(numbers, startIndex)}"
);
Console.WriteLine("press Enter to exit");
readResult = Console.ReadLine();

// This method returns the sum of elements n through 5
static int SumValues(int[] numbers, int n) {
    int sum = 0;
    for (int i = n; i < numbers.Length; i++) {
        sum += numbers[i];
    }
    return sum;
}