How To Get User Input And Create Variable

Okay, so I know how to get user input and create a variable from the input, create a basic addition sum etc...

So I have this code:

package calc;
import java.util.Scanner;
class calc{
private static final double add = 0;
private static final double subtract = 0;
public static void main(String args[]){

[Code] .....

I'm basically trying to make it so that when the user enters tnum, tnum2, tnum3 and tnum4, their answer turns to the variable which has to be either true or false to make the boolean work. I don't know really how to do this. I want to make it so that if they enter yes, then that makes the boolean true and the numbers will multiply and create the answer variable. If they enter no then the boolean is false and it moves onto the next if statement. How can I do this?