Why is BlueJ is giving any answer the same value as I gave in input ?

Question

I have been facing this problem since two months ago. I had written a program which I had declared the variables as 0 or 0.0 as mentioned in the question. When I had executed the program and gave the input(≠ 0), to my great amazement, it came the same result as input, which was very unexpectable . Later, by doing several experiments, I concluded that "It is not doing any operations which I have programmed it to do." How can I resolve it? Here are the codes(Please execute these codes in BlueJ Environment) :
https://code.sololearn.com/c2OzIIWda3T2/?ref=app
https://code.sololearn.com/c49gQqDr34Cf/?ref=app
[Edited: I would like to thank "zemiak" and "~swim~" for their due efforts to make my program successful. I wanted to mark both of their answers as the best answer. But I was not able to do so. So, I marked neither of them as the best answer. What did they said is that I did "int/int(for percentage) * double", which was causing all the troubles. ]

Answer 1

yes, in camera if you use
int / int * double
you lost decimal part of double numbers, so result is different to your expects.

use all numbers with decimal point so fix camera program:
//d = 10 /100 * price;
d = 10.0/100.0 * price;
...
//gst = 6 /100 * dprice;
gst = 6.0 /100.0 * dprice;

then for input 10.0 you get 9.54 as result:
Enter the printed price of digital camera:
10.0
The amount to be paid by the customer:9.54

I check it on BlueJ but I was able only compile it and run it manually in terminal with result 9.54 too

Answer 2

Thank you "zemiak" and "~swim~"!!!

Answer 3

show the code

Answer 4

I have edited in the description but please execute these in BlueJ, especially the "Camera" code, which is again giving catostrophic results.