You just need to build a string to enter in the first parametere of the Visual Basic Shell function.
If you have two text boxes, and the user has entered the appropriate numbers, just use the entered values to build your string for the first parameter of the Shell function.
lngReturn = Shell("c:\cfiles\cfile.exe " & txtNo1.text & " " & txtNo2.text, vbNormalFocus)
Your C++ program should be able to handle the arguments using GetCommandLine(), if using the GUI or argv[] if using a console application.