Dangling-else Problem

The compiler always associates an else with the immediately preceding if unless told to do otherwise by the placement of braces ({ and }). This behavior can lead to what’s referred to as the dangling-else problem. For example,

appears to indicate that if x is greater than 5, the nested if statement determines whether y is also greater than 5. If so, "x and y are > 5" is output. Otherwise, it appears that if x is not greater than 5, the else part of the if...else outputs "x is <= 5".

Beware! This nested if...else statement does not execute as it appears. The compiler actually interprets the statement as

in which the body of the first if is a nested if...else. The outer if statement tests whether x is greater than 5. If so, execution continues by testing whether y is also greater than 5. If the second condition is true, the proper string—"x and y are > 5"—is displayed. However, if the second condition is false, the string "x is <= 5" is displayed, even though we know that x is greater than 5.

To force the nested if...else statement to execute as originally intended, we can write it as follows:

The braces ({}) indicate to the compiler that the second if statement is in the body of the first if and that the else is associated with the first if.