How to replace random number in asp.net/c with pictures?

I am trying to replace random number with pictures. for example If random number is 1 show picture black.jpg:

Cache[diceKey] = r.Next(1, 5);  // random (1-4)

if (r.Next(1, 2) =开发者_运维知识库= 1 )
    image.BackImageUrl = "Images/black.png";

is there any solutions that I can show my picture if random number is 1?

Store your image urls in an array. Generate a random index to access the image:

string[] imageUrls = new [] { "foo.png", "bar.png", "foobar.png" };
// ...
Random r = new Random();
image.BackImageUrl = imageUrls[r.Next(imageUrls.Length)];

Update (still not getting the issue, though)

Only set a certain image if the generated random number is 1:

int i = r.Next(1, 5); // random (1-4)

Cache[diceKey] = i; 

if (i == 1)
{
  image.BackImageUrl = "Images/black.png";
}

As I already said in my comment r.Next(1, 2) will always return 1, so you will always show that black image...

I think you should change your code to this:

var randomValue = r.Next(1, 5);  // random (1-4)
Cache[diceKey] = randomValue;

if (randomValue == 1)
    image.BackImageUrl = "Images/black.png";
else
    image.BackImageUrl = "";