C# Loop Through An Array

You have a collection of strings. The largest string is still a string, not an int. Since s.Max() is a string, and you're assinging it to a variable of type int: int x = s.Max(); the compiler (correctly) informs you that the types do not match. You need to convert that string to an int. Since, looking at your data, they aren't integers, and I see no sensible way of converting those strings into integers, I see no reasonable solution. What integer should "firstitem" be?

If you just want to execute some code for each item in the array then use one of these patterns:

foreach(string item in s)
{
    System.Diagnostics.Process.Start("www.website.com/" + item);
}

or

for(int i = 0; i < s.Length; i++)
{
    System.Diagnostics.Process.Start("www.website.com/" + s[i]);
}

1. You're missing a couple of semi-colons
2. x should presumably be the Length of the array, not the largest value in it
3. You need to increment x inside of your loop - at the end of it, not outside of it
4. You should actually be incrementing n, not x
5. n should be starting at 0, not at 1
6. Inside the loop you're using b[0] where you probably want to use b[n]
7. I'm no C++ guru, but I have no idea what b[]++ might mean
8. As other answers have mentioned, you may want to use a for or foreach instead of a while.
9. Make an effort to go through some introductory tutorials. Trial and error can be a useful tool, but there's no need to fall back on that when learning the very basics

from the sample

var processList = (new string[]{"firstitem","seconditem","thirditem"})
                 .Select(s => Process.Start("www.website.com/" + s))
                 .ToList();

and here is a test version that outputs to console

(new string[] { "firstitem", "seconditem", "thirditem" })
          .Select(s => {  Console.WriteLine(@"www.website.com/" + s); return s; })
          .ToList();

note: Select requires a return type and the .ToList() enforces evaluation.

Following is an image to point out what are the errors of your code:

After the correction, it would be:

int n=1;
string[] s= { "firstitem", "seconditem", "thirditem" };
int x=s.Length;

while(n<x) {
    System.Diagnostics.Process.Start("www.website.com/"+s[n]);
    n++; // or ++n
}

And we can make it more semantic:

var items=new[] { "firstitem", "seconditem", "thirditem" };

for(int index=1, count=items.Length; index<count; ++index)
    Process.Start("www.website.com/"+items[index]);

If the starting order doesn't matter, and we can use foreach instead, and we can use Linq to make the code even simpler:

var list=(new[] { "firstitem", "seconditem", "thirditem" }).ToList();
list.ForEach(item => Process.Start("www.website.com/"+item));

and we might quite often write in another form:

foreach(var item in new[] { "firstitem", "seconditem", "thirditem" })
    Process.Start("www.website.com/"+item);