Get return value from process

Hi I am trying to do the following: I have a process which can take parameters (digits) and return the sum of these numbers

Process P = Process.Start(sPhysicalFilePath, Param);
                int result = P.ExitCode;

I get the return value from "ExitCode" the problem is: the program sometimes finishes his work before the process so when the program reaches this line

int result = P.ExitCode;

I got an exception .. my question is how to wait this process until it finishes its work sorry I forget to say that's I am working with C# language

Solution 1:

use:

Process P = Process.Start(sPhysicalFilePath, Param);
P.WaitForExit();
int result = P.ExitCode;

from MSDN