[DrJava] [ drjava-Bugs-1091541 ] Mathematical evaluation

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Bugs item #1091541, was opened at 2004-12-26 18:03
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Category: Compiler integration
Group: Could cause data loss
Status: Open
Resolution: None
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
Summary: Mathematical evaluation

Initial Comment:
Entering: (10+(2*3))*(2^(1+2))
into the interaction window gives the faulty result of '16' 
when it should be 128. This is quite likely due to the 
statement being incorrectly parsed in terms of 
parenthesis. 

I ran across an identical error writing a calculator 
program. In parsing the statement in broke the 
statement down recursively and was then attempting to 
evaluate (1+2)). This evaluated to 0 instead of three, 
causing the entire statement to evaluate incorrectly to 
16. 

I fixed this in my own program by carefully rewriting the 
loop that counted parenthesis as so:

This loop ensured that inner items were processed first. 
In doing so it kept a count of how many parenthesis it 
had passed, +1 for a left paren, and -1 for a right 
paren. Having the imbalance in the expression, that is 
one left paren and two right paren's messed up the 
count, and the inner expression 1+2 was never 
evaluated, but returned '0'.

This bug is visible in the interactions pane, as well as a 
System.out.println command in an actual java class. 
-jack

JH...@gm...


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