String split C#

1.)string split C#
string str = null;
string[] strArr = null;
int count = 0;
str = "CSharp split test";
char[] splitchar = { ' ' };
strArr = str.Split(splitchar);
for (count = 0; count < = strArr.Length - 1; count++)
{
MessageBox.Show(strArr[count]);
}

2.)RELACE STRING

string str = "This test";
// Replace string
str = str.Replace("is", "was");

3.)