The-C-Programming-Language | The practices for K & R `` The C Programming Language | Learning library
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The practices for K&R "The C Programming Language"
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QUESTION
I am writing a function that is supposed to populate an array with random numbers from 0 to n (where n is passed argument to the function), but all numbers in array should be unique. I basically need to shuffle the array of numbers from 0 to n
I found this answer here: Unique random numbers in an integer array in the C programming language
And used the "Knuth Algorithm" suggested by user:
...ANSWER
Answered 2019-Mar-12 at 12:54A C implementation example of the algoritm is as follows in the answer you quoted:
QUESTION
I have looked into several topics to try to get some ideas on how to make a reliable clock with C or C++. However, I also saw some functions used the processor's ticks and ticks per second to calculate the end result, which I think could be a problem on a CPU with auto-overclock like the one I have. I also saw one of them reset after a while, thus is not really reliable.
The idea is to make a (preferably cross-platform) clock like an in-game one, with a precision better than a second in order to be able to add the elapsed time in the "current session" with the saved time at the end of the program. This would be to count the time spent on a console game that does not have an in-game clock, and on the long run to perhaps integrate it to actual PC games.
It should be able to run without taking too much or all of the CPU's time (or a single core's time for multi-core CPUs) as it would be quite bad to use all these resources just for the clock, and also on systems with auto-overclock (which could otherwise cause inaccurate results).
The program I would like to implement this feature into currently looks like this, but I might re-code it in C (since I have to get back to learning how to code in C++):
...ANSWER
Answered 2017-Dec-26 at 15:38The std::chrono::high_resolution_clock
seems to be what you are looking for. On most modern CPUs it is going to be steady monotonically increased clock which would not be affected by overclocking of the CPU.
Just keep in mind that it can't be used to tell time. It is only good for telling the time intervals, which is a great difference. For example:
QUESTION
I have the following situation: I would like to generate M=500,000 unique random numbers between 1016 and 264-1. To simplify the situation, we can assume, that we need a number between 1 and N=264-1.
I already found references to this question >here< and >here< and >here<.
But I still have the feeling, that the methods mentioned in the references work if N is much smaller. I.e. it is no option to make a list of all numbers from 1 to N, mix them and take the first M. And somehow I think that there should be a much more effective way than try and error, since M<< N. And M<< N are always given. Therefore the algorithm has not to be good if N-M is small or even N=M. But somehow the big N gives me headache...
Related to this problem I tried to expand qrand() to get a random `quint64 with
...ANSWER
Answered 2017-Jun-16 at 16:212^64-1 is a 64 bit number. DES uses a 64 bit block size. Using a fixed key, encrypt the numbers 0, 1, 2, 3, 4, ... with DES in ECB mode for as many numbers as you need. Because the inputs are unique and the key is fixed the 64-bit outputs are also guaranteed unique.
If a 64-bit number is < 10^16 just reject it and go on to the next input integer. That will happen about 1 in every 1,800 numbers (2^64 / 10^16).
If you record the key and the last number used you can add more numbers to the list as needed.
I assume there is a C++ DES implementation you can run from Qt.
QUESTION
I am reading "The C programming Language" by Brian W. Kernighan and Dennis M. Ritchie. In chapter 1.2 "Variables and Arithmetic Expressions" they demonstrate a simple Fahrenheit to Celsius converter program. When I compile the program (Terminal.app, macOS Sierra), I get this warning:
...ANSWER
Answered 2017-May-06 at 10:02Just give main
a return type:
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