How To Make Replacements

i have vb10 and i maid a form that contains richtextbox and button1 and label1

i want to type something in the richtextbox1

when i press the button1 i want it to take a litter by litter and convert each one to other character or numbers which the modified text will be in label1

the problem is i could change except the last command in the button1

for example :i but this code , which is in button1_click:-

label1.text= richtextbox1.text.replace("a",",10,") label1.text= richtextbox1.text.replace("b",",11,")