How to use value of field for other field in node ?

For exam I have node type A has 2 fields :
"name" and "action", When I fill in name field "My Name", I want the "action" field has value is "Hello Tung!, nice to meet you",
in another exam:
I using cck_table field in my node_type (named "A")
and I have "quantity field"
in my textarea in cck_table I type
"
Name : My Name
Age : My age
Quantity : //How can I use the value of quantity field here
"
thank in advance. sory for my bad english