Using Console.ReadLine().Split() to fill a string array in a loop

Question

I have the following very basic code:

static void Main(string[] args)
{
    int n = Convert.ToInt32(Console.ReadLine());

    for (int i = 0; i < n*3; i++)
    {
        string[] numbers = Console.ReadLine().Split();
        Console.WriteLine();
        Console.WriteLine(numbers[i]);
    }
}

It's supposed to take the following data:

It is taking the first number to determine the number of lines of data their are (there is a reason for this but outside of the scope of this question.
The loop should take line 2, 3 and 4 and populate the numbers array, splitting the data up so numbers[0] = 11, numbers[1] = 9, numbers[2] = 1... and so on. What I'm seeing is that it's putting the first number in the line into the array and moving on. Here is a preview of what it's doing currently:

I was hoping the output would be:

I'm probably doing something completely stupid and blatantly obvious but I'm still trying to learn C#.

"What I'm seeing is that it's putting the first number in the line into the array and moving on." No, it's putting everything into the array - but then you're only printing one number before moving on. How would you expect Console.WriteLine(numbers[i]); to print multiple numbers? — Jon Skeet
– Jon Skeet, Commented Jun 23, 2020 at 9:44
because I'm assuming that it's running the loop 9 times.. one for each number in the array? is it adding the numbers to the array in bulk? — TheRealDax
– TheRealDax, Commented Jun 23, 2020 at 9:46
But it's running the whole of the loop 9 times - so it's reading 9 lines from the console, and printing one number from each of those lines. It sounds like that's not what you wanted. I suggest you step through the code in a debugger, looking carefully at the values at each step. — Jon Skeet
– Jon Skeet, Commented Jun 23, 2020 at 9:48
Try to run the program and enter Banana instead of a number. See what's going on there. — Zohar Peled
– Zohar Peled, Commented Jun 23, 2020 at 12:23

score 1 · Accepted Answer · 2020-06-23 12:47:42Z

Let's go step by step :

You enter 3 so n = 3 and the code in the for loop will run 3 * 3 = 9 times.
You enter 11 9 1 so string[] numbers = { "11", "9", "1" };.
Then it will print a blank line.
Since i = 0 now, it will print numbers[0] which is "11"(It will print 11).

The output is the following at this time:

You enter 14 90 232, so string numbers = { "14", "90", "232" };.
Blank line
Now it's the second time we're going through the loop and i = 1. So it will print numbers[1] which is "90".

The output is the following at this time:

You enter 111 15 111, so string numbers = { "111", "15", "111" };.
Blank line
Now it's the third time we're going through the loop and i = 2. So it will print numbers[2] which is "111".

The output is the following at this time:

You will encounter an error if you enter something like 1 2 3 which contains three numbers, because it will be the forth time we will be going through the loop and i = 3 and since numbers contains three elements you will see the following:

System.IndexOutOfRangeException: 'Index was outside the bounds of the array.'

I recommend string.Join() to get your expected result.

Here's the solutions:

static void Main(string[] args)
{
    int n = Convert.ToInt32(Console.ReadLine());

    for (int i = 0; i < n*3; i++)
    {
        string[] numbers = Console.ReadLine().Split();
        Console.WriteLine();
        Console.WriteLine(string.Join(" ", numbers));
    }
}

Durgesh Pandey · Accepted Answer · 2020-06-23 12:21:10Z

As i see, your numbers array is inside the loop, so every time the loop goes for an iteration, the array is reinitialized, so yes - your program does put all the numbers in the array but only prints the ith element, and even if it runs 9 times, it'll initialize the array 9 times (quite a big thing though). Below is a simpler and more easier for of your code.

static void Main(string[] args)
{
    int n = Convert.ToInt32(Console.ReadLine());
    string numbers[3];

    // read n lines, one by one
    for (int i = 0; i < n; i++)
    {
        numbers = Console.ReadLine().Split();
        Console.WriteLine();

        // print the 3 numbers, either using a smaller loop or simply indexing        
        // I use a loop here to make it more dynamic

        for (int j = 0; j < 3; j++) {
            Console.WriteLine(numbers[j] + " ");
        }
    }
}

though i do not exactly understand your expected output. Do you want to display the last printed line again? If yes, you can simple print the numbers array before reading the new numbers into it (make sure it is not empty, using a boolean flag or something).

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