4.5 How to find the match with nested if... else?

A. Introduction

Take a look at the "else" statement in the code snippet below, which "if" statement does it match to?

double shippingCharge = 5.00; // $5 inside continental U.S. 
if (country.equals("USA"))  
  if (state.equals("HI"))  shippingCharge = 10.00; // Hawaii is more expensive 
else // Pitfall!  
  shippingCharge = 20.00; // As are foreign shipments

The indentation level seems to suggest that the else is grouped with the test country. equals("USA"). Unfortunately, that is not the case. The compiler ignores all indentation and matches the else with the preceding if. That is, the code is actually

double shippingCharge = 5.00; // $5 inside continental U.S. 
if (country.equals("USA"))  
    if (state.equals("HI"))
      shippingCharge = 10.00; // Hawaii is more expensive  
    else // Pitfall!
      shippingCharge = 20.00; // As are foreign shipments

That isn’t what we want. You want to group the else with the first if. The ambiguous else is called a dangling else. You can avoid this pitfall if you always use braces, as below:

double shippingCharge = 5.00; // $5 inside continental U.S.
 if (country.equals("USA"))
  { // beginning of the if block
   if (state.equals("HI")) {  shippingCharge = 10.00; // Hawaii is more expensive  }
  } // end of the if block
  else {  shippingCharge = 20.00; // As are foreign shipments }

The brace in bold faces marks the beginning and end of the first "if" block, allows the "else" to match the first "if" instead of the second.

B. Notes : "else" is always matched to the closest "if block"