"so what kinda of tips can you give me for the following code."
Break everything down to individual tasks, then work on one at a time
eg
write a program to get customer numbers (with an exit routine)
compile/run - you will discover an error at "showInputDiaolg("
fix/compile/run
when this is working, include getting kwh
complie/run/fix/compile/run etc
add findCharge()
test, when OK
add increments to cumulatives
test
add output method
test
when OK
feet up, take a break.