Equivalent of this C/C++ program in C#

Question

In high school I've studied basic C/C++ (it basically was C with cin and cout - those were the only C++ things, so I'd rather say I've been studying C in my high school time)

Now that I'm in college, I have to transition to C#.

I'm currently trying to make this C program in C#.

int main()
{
    int array[100];
    for (int i = 0; i < 5; i++)
    {
        cin >> array[i];
    }
    for (int i = 0; i < 5; i++)
    {
        cout << array[i] << " ";
    }
}

Here is how I tried to write it using C#:

using System;
using System.Linq;

namespace ConsoleApp2
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] array = new int[100];
            for (int i = 0; i < 3; i++)
            {
                array[i] = Convert.ToInt32(Console.ReadLine());
            }
            for (int i = 0; i < 3; i++)
            {
                Console.WriteLine(array[i]);
            }
        }
    }
}

and it's kind of similar but it has a problem that I don't know how to fix.

In C, building that program, I could've entered data like this: In C#, I can't, because I'm getting an exception:

I kind of understand what's happening - in C#, using Console.ReadLine() reads that line as a string, and then it tries to convert into an integer.

That does fail because of the spaces between the digits - "1 2 3".

But in C this works, because cin works differently, I guess. (I don't know how though and at this point I don't care anymore, I probably won't be using C/C++ anymore).

How can I replicate this behavior of the C program in the C# program so I can enter data as I did in the pic?

Answer 1

The main problem here is that you're using Console.ReadLine instead of Console.ReadKey. cin >> array[i] will attempt to get the next int from stdin (thanks @UnholySheep), not the next line, so the equivalent of it would be Console.ReadKey().KeyChar with manual type conversion.

Now, there are multiple ways of converting a char to an int in C#, but casting isn't one as it would result in wrong conversions (in C# (int) '1' == 49, proof). My preferred way is int.TryParse(char.ToString(), out int number), but some people use different methods.

Edit: This will only handle single digit input correctly. If you need multi digit input, see the end of the answer.
This means, your code turns into this:

var array = new int[5];
for (var i = 0; i < 5; i++)
{
    var read = Console.ReadKey().KeyChar.ToString();
    if (int.TryParse(read, out var number))
        array[i] = number;

    Console.Write(" ");
}

foreach (var element in array)
{
    Console.Write("${element} ");
}

Note that I emulated the space between your input by writing an empty space in between every Console.ReadKey call. I also decided to foreach over the array as well as used string interpolation ($"{...} ...") to print the element with a space next to it.
If you want to manually enter the spaces, you can leave out the Console.Write(" ");, but then be aware that the array will contain a number only every other element, and the rest will contain 0 (default value of int)

---

To correctly handle multi digit input, you can either:

1. Use Console.ReadLine and live with the fact that multiple inputs need to come on different lines
   or
2. Use some botched together method to read the next int from the Console. Something like this:

public static int GetNextInt()
{
    var totalRead = new List<char>();

    while(true)
    {
        var read = Console.ReadKey().KeyChar;
        if (!char.IsDigit(read))
        {
            if (totalRead.Count > 0)
                break;
        }
        else
            totalRead.Add(read);
    }

    if (totalRead.Count == 0)
        return -1;

    return int.Parse(new string(totalRead.ToArray()));
}

This will try it's hardest to get the next int. Some test cases are:

+---------+-------------------+
|  Input  |    Parsed int     |
+---------+-------------------+
| "123\n" | 123               |
| "123a"  | 123               |
| "a123a" | 123               |
| "a\n"   | Continues parsing |
| "\n"    | Continues parsing |
+---------+-------------------+

There is currently some redundant code, but you can remove on or the other line depending on what you want.

1. Do you want the current functionality?
   Then you can safely remove if (totalRead.Count == 0) return -1;

2. Do you want the method to return -1 if the first entered character isn't a number?
   The you can safely remove if (totalRead.Count > 0) but keep the break.

My goal with this wasn't to 1:1 copy the C++ functionality of std::cin >> ..., but to come close to it.

Answer 2

This does exactly what you want, what you need is Console.Read() function :

    public static void Main(string[] args)
    {
        int[] array = new int[100];
        int index = 0;

        for (int i = 0; i < 3; i++)
        {
            string word = string.Empty;
            bool isNew = true, assigned = false;
            while (isNew)
            {
                char read = (char)Console.Read();

                if (!char.IsDigit(read))
                {
                    if (isNew && assigned)
                    {
                        array[index++] = int.Parse(word);
                        isNew = false;
                    }
                }
                else
                {
                    word += read;
                    assigned = true;
                }
            }
        }

        for (int i = 0; i < 3; i++)
        {
            Console.Write(array[i] + " ");
        }

        Console.WriteLine();
    }

You can also take a look at :

https://nakov.com/blog/2011/11/23/cin-class-for-csharp-read-from-console-nakov-io-cin/