如何替换字符串

Question

字符串：
aaaBaaaBaaaaBaaaaBaaa............共有10个B
如何替换第二个和第四个的B为C

Answer 1

还真麻烦，又没规律
string tmp="aaaBaaaBaaaaBaaaaBaaa............ ";
string[] arrTmp=tmp.split('B');
StringBuilder strBuilder=new StringBuilder ();
for(int iCount=0;iCount<arrTmp.Length;iCount++)
{
   strBuilder.Append( arrTmp[iCount]);
   if(iCount=1 || iCount=3) strBuilder.Append("B");
}
strBuilder.ToString()为所求