WhySave

You get a call from a new Phone number and then for some reason you need to send them your location or some file using WhatsApp. And WhatsApp on smart phones doesn't have a feature built rite into it to start a conversation with unsaved phone numbers. Using this app you can do it in split seconds. You don't have to save/delete unnecessary numbers on your phone anymore. You need not have to worry about your privacy while using this app because it's source code is available on GitHub.

To use this app,
open the app and select the country code of that number using the dial, then type the number and click on that button, now select WhatsApp (select always for WhatsApp to make it seamlessly open every time)
if the country code isn't available on dial then type the country code before typing that number.
or
swipe left to access right tab where you can see your previous calls list (for which you need to give the permission in the beginning rite after opening the app), tapping on the numbers will directly take you to WhatsApp conversation with that number.