Sorry, the checksum is sent as an ascii character as well in the string. Here is a synopsis of how I got here.
My initial transmission was going to be V;RB4.75;I123456 for example (based on Sensus water meter protocol).
The radio vendor replied that they can not support the ascii character "." in the RB field "quote below" and they don't use the I field so it's not needed
"1. “V;RB0475;;”. We can’t use the ASCII “.”. The checksum is one byte of exclusive-ORs of all previous bytes e.g. V;RB0475;"
Memory leaks aren't a big concern for me because of the way this will work. The radio will provide me a burst of 5.6v for a period of time (let's say 1 second). During that time the chip needs to wake up, take the hall effect read, ans transmit back via a quasi Sensus protocol message the value of the read. Then power is turned off and it waits for the next cycle. There is no low-level voltage that keep the chip in sleep mode during the down cycle.
I am using the Arduino right now just as a proof of concept and ultimately want to put a chip inline between the radio and hall effect sensor.
I'll research 'C' strings , thanks for the tip.