Re: "undefined behavior"?

On 12/06/2024 21:47, DFS wrote:

Wrote a C program to mimic the stats shown on:
 https://www.calculatorsoup.com/calculators/statistics/descriptivestatistics.php
 My code compiles and works fine - every stat matches - except for one anomaly: when using a dataset of consecutive numbers 1 to N, all values  > 40 are flagged as outliers.  Up to 40, no problem.  Random numbers dataset of any size: no problem.
 And values 41+ definitely don't meet the conditions for outliers (using the IQR * 1.5 rule).
 Very strange.
 Edit: I just noticed I didn't initialize a char:
before: char outliers[100];
after : char outliers[100] = "";
 And the problem went away.  Reset it to before and problem came back.
 Makes no sense.  What could cause the program to go FUBAR at data point 41+ only when the dataset is consecutive numbers?

I assume outliers is inside a function.
What are the 100 values of outliers if you don't initialise it? You can try printing them out (as individual numbers not as a string) although just doing that, and adding that extra code, may change the actual values.
However that doesn't matter if it still goes wrong; you may still get a hint as to why it's behaving as it is.

Also, why doesn't gcc just do you a solid and initialize to "" for you?

Initialising to "" will zero the entire array. You really want the compiler to do that work, even when you're going to overwrite it anyway?