You need to use an infile.clear() call, since you are working with same ifstream object throughout the program. See
http://www.cplusplus.com/reference/iostream/ios/clear.html
Try also to understand and learn how to use the eof(), fail(), good() functions.
case 7:
infile.open(myFile.c_str(), ios::in);
[B]infile.clear();[/B]
Note that, when you add words to the file, add a newline also, otherwise you'll have just one long word.