Ever stumbled upon a weird problem and couldn’t quite figure out where things went wrong?
I’ve been there, and so has a friend of mine while tackling a HackerRank challenge.
The task seemed simple: take a mathematical expression as input and print out the result with three decimal places.
However, getting there wasn’t as straightforward as expected.
Let’s walk through what happened and how we can apply the lessons learned to similar problems.
The Initial Problem
The challenge required reading an expression from the input and then outputting the result to three decimal places. My friend’s first attempt looked like this:


However, one test case failed due to being off by 0.001. This tiny discrepancy was a significant clue that the approach to handling decimal precision and rounding needed reevaluation.
Side Note
Although this is a personal style preference, the usual way I would pipe a string intobc
would involve echoing the string or using a heredoc, not directly using the$(())
syntax.A better version might look like this:
1 2
read var echo "scale=3; $var"  bc
I suggested increasing the scale
to 4 (scale=4
) to explore the behavior, which led to failing all test cases. It seemed counterintuitive, but the point was to dig deeper into how the bc
command processes numbers.
What We Discovered
After running some tests locally (always a good practice before submitting your solution), we noticed something interesting:


The exploration revealed a crucial detail: bc
truncates rather than rounds numbers when applying the scale
. That’s where the printf
function becomes handy.
The Practical Solution
The workaround is to use bc l
for the calculation to ensure full precision and then printf "%.3f\n"
to format the output correctly, rounding to three decimal places.
Key Takeaways
 Precision Matters: The failure of a test case by just 0.001 should immediately signal that the handling of decimal precision and rounding is critical.
 Test Locally: Always run your code locally first (unless it’s impossible of course!). It helps catch errors and understand the problem better.
 Know Your Tools: Understanding how commands like
bc
andprintf
work is crucial.bc
sets the number of decimal places but doesn’t round, whileprintf
can format and round the output.  Experiment and Learn: Don’t be afraid to change your approach. Testing with a
scale
of 4 revealed howbc
handles precision.  Pay Attention to Details: Small discrepancies can point to larger issues. A mismatch of 0.001 isn’t just a minor error; it’s an indicator that your method of handling precision needs adjustment.
When you face a coding challenge, keep these insights in mind.
Sometimes, the solution involves more than just writing the code; it’s about understanding the behavior of the tools at your disposal.
Happy coding! Have you ever faced a similiar problem before? Tell me all about it!