How can I convert different choices to numeric values?

I would like to inquire about the calculation matter. I want ask a question that requires to select from (yesnolist) and the answer will be yes or no or something . Now, the question is "Is there a formula for each question to calculate the answer as number. For example, if the answer will be (yes), the calculation will be (2) and if the answer is (no), the calculation will be (0) and so on. If there is such calculation, would you please clarify this point in a test excel sheet. Another thing is to calculate all questions in the group and what if i have more than one group and want to calculate the groups.
test (calcuation).xls (27.5 KB)

If the answer X is (yes) then the calculation is Y+1, otherwise the calculation is Y-1, can be expressed as:

if(${x}='yes', ${y}+1, ${y}-1)

Or more generally, if answer X is (a) then calculation is foo, or if X is (b) then bar, or if X is (c) then qux, or...

if(${x}='a', foo, if(${x}='b', bar, if(${x}='c', qux, ...)))

ie use nested if's