C# - Why the unstable "Random"?

Question

C++ / C#

There was a problem with the "Random" function. Sometimes it doesn't show results. Essence: I made a "random" number from 1 to 100, and then I wrote with the help of "if" what will happen if certain numbers fall out. And when testing, sometimes the result was not displayed, I decided to check, I wrote else { Console.WriteLine("Error") }:. As a result, with a fairly good chance, it gives Error ... What's the problem? Here is the code:

Random rnd1 = new Random();

if (rnd1.Next(0, 100) == 1 || rnd1.Next(1, 100) == 2 || rnd1.Next(1, 100) == 3 || rnd1.Next(1, 100) == 4 || rnd1.Next(1, 100) == 5 || rnd1.Next(1, 100) == 6 || rnd1.Next(1, 100) == 7 || rnd1.Next(1, 100) == 8 || rnd1.Next(1, 100) == 9 || rnd1.Next(1, 100) == 10 || rnd1.Next(1, 100) == 11 || rnd1.Next(1, 100) == 12 || rnd1.Next(1, 100) == 13 || rnd1.Next(1, 100) == 14 || rnd1.Next(1, 100) == 15 || rnd1.Next(1, 100) == 16 || rnd1.Next(1, 100) == 17 || rnd1.Next(1, 100) == 18 || rnd1.Next(1, 100) == 19 || rnd1.Next(1, 100) == 20 || rnd1.Next(1, 100) == 21 || rnd1.Next(1, 100) == 22 || rnd1.Next(1, 100) == 23 || rnd1.Next(1, 100) == 24 || rnd1.Next(1, 100) == 25 || rnd1.Next(1, 100) == 26 || rnd1.Next(1, 100) == 27 || rnd1.Next(1, 100) == 28 || rnd1.Next(1, 100) == 29 || rnd1.Next(1, 100) == 30 || rnd1.Next(1, 100) == 31 || rnd1.Next(1, 100) == 32 || rnd1.Next(1, 100) == 33 || rnd1.Next(1, 100) == 34 || rnd1.Next(1, 100) == 35)
            {
                Console.WriteLine("1");
            }
            else if (rnd1.Next(0, 100) == 36 || rnd1.Next(1, 100) == 37 || rnd1.Next(1, 100) == 38 || rnd1.Next(1, 100) == 39 || rnd1.Next(1, 100) == 40 || rnd1.Next(1, 100) == 41 || rnd1.Next(1, 100) == 42 || rnd1.Next(1, 100) == 43 || rnd1.Next(1, 100) == 44 || rnd1.Next(1, 100) == 45 || rnd1.Next(1, 100) == 46 || rnd1.Next(1, 100) == 47 || rnd1.Next(1, 100) == 48 || rnd1.Next(1, 100) == 49 || rnd1.Next(1, 100) == 50 || rnd1.Next(1, 100) == 51 || rnd1.Next(1, 100) == 52 || rnd1.Next(1, 100) == 53 || rnd1.Next(1, 100) == 54 || rnd1.Next(1, 100) == 55 || rnd1.Next(1, 100) == 56 || rnd1.Next(1, 100) == 57 || rnd1.Next(1, 100) == 58 || rnd1.Next(1, 100) == 59 || rnd1.Next(1, 100) == 60 || rnd1.Next(1, 100) == 61 || rnd1.Next(1, 100) == 62 || rnd1.Next(1, 100) == 63 || rnd1.Next(1, 100) == 64 || rnd1.Next(1, 100) == 65)
            {
                Console.WriteLine("2");
            }
            else if (rnd1.Next(0, 100) == 66 || rnd1.Next(1, 100) == 67 || rnd1.Next(1, 100) == 68 || rnd1.Next(1, 100) == 69 || rnd1.Next(1, 100) == 70 || rnd1.Next(1, 100) == 71 || rnd1.Next(1, 100) == 72 || rnd1.Next(1, 100) == 73 || rnd1.Next(1, 100) == 74 || rnd1.Next(1, 100) == 75 || rnd1.Next(1, 100) == 76 || rnd1.Next(1, 100) == 77 || rnd1.Next(1, 100) == 78 || rnd1.Next(1, 100) == 79 || rnd1.Next(1, 100) == 80 || rnd1.Next(1, 100) == 81 || rnd1.Next(1, 100) == 82 || rnd1.Next(1, 100) == 83 || rnd1.Next(1, 100) == 84 || rnd1.Next(1, 100) == 85)
            {
                Console.WriteLine("3");
            }
            else if (rnd1.Next(0, 100) == 86 || rnd1.Next(0, 100) == 87 || rnd1.Next(0, 100) == 88 || rnd1.Next(0, 100) == 89 || rnd1.Next(0, 100) == 90 || rnd1.Next(0, 100) == 91 || rnd1.Next(0, 100) == 92 || rnd1.Next(0, 100) == 93 || rnd1.Next(0, 100) == 94 || rnd1.Next(0, 100) == 95 || rnd1.Next(0, 100) == 96 || rnd1.Next(0, 100) == 97 || rnd1.Next(0, 100) == 98 || rnd1.Next(0, 100) == 99 || rnd1.Next(0, 100) == 100)
            {
                Console.WriteLine("4");
            }
            else
            {
                Console.WriteLine("Error");
            }
            string theEnd = Console.ReadLine();

Answer 1

Because every time there is a comparison with a new random number.
In general, to admit, for such a code I want to tear something off =))))
...

Console.WriteLine((new Random()).Next(1, 4).toString());

Answer 2

The author most likely needs to apply weight coefficients to each element
. All this can be done a little easier through the list of weights (the number of entries was taken from the ceiling):

var probabilityList = new List<string>();
probabilityList.AddRange(Enumerable.Repeat("1", 40));
probabilityList.AddRange(Enumerable.Repeat("2", 30));
probabilityList.AddRange(Enumerable.Repeat("3", 20));
probabilityList.AddRange(Enumerable.Repeat("4", 10));

var rnd = new Random();
var randomItem = probabilityList[rnd.Next(probabilityList.Count)];

Answer 3

You misunderstood the logic from the question. You need to first enter the result of the randomization into a variable, and then compare it. Huh)

Random rnd1 = new Random();
int i = rnd1.Next(0, 100); // присвоили значение рандома
// а теперь проверяете if'ами
if (i == 86) //...
if ((i == 74) || (i == 64) ...)) ...