Functioning if statement, improving it - if-statement

Question

if (dog.equalsIgnoreCase("yes")) {
drink.don.setCost(8.75);
drink.don.getType();
drin.l.add(drink.don.getType());
drink.c.add((double) coke.don.getCost());
cokeprice = coke + fanta.don.getCost();
else if (dog.equalsIgnoreCase("no"))
else catch(IllegalArgumentException iae) {
System.out.println("requires yes or no");
}
}
Ignore the stupid naming conventions had to change them, incase any class mates decided to steal anything ;p
I'm trying to get my if statement to allow the user input yes and do a condition, then if "no" has been entered then nothing happens just moves onto the next statement, then anything else is illegal and the program crashes.

Answer 1

I don't like throwing exceptions, especially if I expect that the user might type in something that I don't want. I'd rather do something like
if (userInput.equalsIgnoreCase("Yes")) {
// do yes
}
else if (userInput.equalsIgnoreCase("No")) {
// do no
}
else {
// Sorry, invalid input
}

Answer 2

I don't know what language you are using, nor do I know what any of the methods you are using do, but here is an example of a similar statement in C#.
First, use a method to convert the user input to a true or false (boolean) value:
public static bool IsYes (string userInput)
{
if (userInput == "yes')
{
return true;
}
else if (userInput == "no")
{
return false;
}
else
{
throw new CustomException();
}
}
Next, you can take the result of IsYes() and use it for the if else statement:
if (IsYes(userInput))
{
// code you want to execute if "yes"
}
else
{
// code you want to execute if "no"
}
Hopefully this code will give you an idea of how to use if-else statements, but in the future please explain your question more clearely. Remember, this is C#, so although if statements are similar in almost all languages some of the other code will differ. Also, this is just an example, it won't do anything on its own.