No need to declare extra variables and inside the loops. Try the following code to divide you first and second result:
string mExp = "3/2/1/2";
string[] strNum = (Regex.Split(mExp, @"\s*[+/*-]\s*"));
List<string> stringList = mExp.Split('/').ToList();
int i;
decimal c, d, e = 0;
for (i = 0; i < stringList.Count - 1; i++)
{
c = int.Parse(stringList[i]);
d = int.Parse(stringList[i + 1]);
if (i == 0)
e = c / d;
else
{
e /= c / d;
}
i++;
}
Console.WriteLine(e);
Console.ReadLine();