There is one question in my mind. What's the logic behind rand function. That is how can we write our own rand function.
One approach may be to use garbage value of variables
But problem with this code is that it will always print same numbers. Is garbage value a fixed value at a memory location. That is say at memory location X if not initialised i will get same value each time. What can be reason behind this?Code:int main() { int a[10]; for(int i=0;i<=10;++i) cout<<a[i]; }
> One approach may be to use garbage value of variables
1. even reading undefined values may cause exceptions
2. you run off the end of the array
Common implementations of rand() use this
http://www.physics.orst.edu/~rubin/n...mc3/node2.html
Such algorithms are only any good for student exercises.
For statistical quality rand functions, consider this one
http://www.math.sci.hiroshima-u.ac.j...at/MT/emt.html
For cryptographic quality rand functions, you really need an entropy pool based approach, like
http://publib.boulder.ibm.com/infoce...les/random.htm
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
I suggest that you read what Prelude has to say about Random Numbers.
Look up a C++ Reference and learn How To Ask Questions The Smart WayOriginally Posted by Bjarne Stroustrup (2000-10-14)
It is very surpising and shoking to see that there is same garbage value at a position in main memory. No matter how many times I run above program I get same result?
Any idea why it is so
Because your program happens to read from the same memory location each time it is run? I do not think that this is the right approach especially since the contents of memory may not have very random properties to begin with.It is very surpising and shoking to see that there is same garbage value at a position in main memory. No matter how many times I run above program I get same result?
Any idea why it is so
Look up a C++ Reference and learn How To Ask Questions The Smart Way
Yup.
If I did your homework for you, then you might pass your class without learning how to write a program like this. Then you might graduate and get your degree without learning how to write a program like this. You might become a professional programmer without knowing how to write a program like this. Someday you might work on a project with me without knowing how to write a program like this. Then I would have to do you serious bodily harm. - Jack Klein
Some people call them 'pseudo-random numbers', but they are still in a state of sin either way
Look up a C++ Reference and learn How To Ask Questions The Smart Way
But even after restarting my computer,I get same result. Is it such that garbage value is constant for a particular memory location.Code:Because your program happens to read from the same memory location each time it is run?
Do yourself a big favor and don't try to read variables that don't store anything yet. (Okay an array could be called one variable, but don't pick on me; it's a collection of variables the same size given a single name.) It's dangerous.
Your BIOS runs a RAM test every time you start your computer. The data may be left-over from the RAM test, or it may be left-over from something that Windows was doing during start-up.But even after restarting my computer,I get same result. Is it such that garbage value is constant for a particular memory location.
I'll bet if you did a statistical analysis of all the numbers in memory, some numbers would show-up more frequently than others. Small numbers would be more common than large numbers. Numbers that represent ASCII characters would be common. Numbers that represent CPU op-codes would be common, etc.
Hmm...,that seems to be quite logical.But can I check it
Also, in debug mode, the compiler tends to insert code to fill memory with known values, just so that it can check a few things.
All the buzzt!
CornedBee
"There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
- Flon's Law
Good suggestions, Salem!
I would like to add (if the OP is open to more suggestions) that NETLIB has many random number generation routines. They happen to be written in FORTRAN, but they are pretty easy to translate into C++.
Also, Boost has some random number libraries too:
Boost Link
Regards,
David
a couple of years ago (when it released the p3) intel was talking about implementing a rand assembly instruction that took a truly random physical value (chip heat, electrical interference,etc) and returned it. Anyone ever hear what happened to that?
BTW if you want a truly random value, get a geiger counter and some radioactive material and hook it up to your pc.
"I saw a sign that said 'Drink Canada Dry', so I started"
-- Brendan Behan
Free Compiler: Visual C++ 2005 Express
If you program in C++, you need Boost. You should also know how to use the Standard Library (STL). Want to make games? After reading this, I don't like WxWidgets anymore.Want to add some scripting to your App?
www.random.org
But please be polite, and don't use up all of them
rand() uses a math algorithm, which doesn't provide true random numbers, but a sequence of numbers which at first glance APPEAR to be random, and pass statistical tests that random numbers pass.
You could read up on the Mersenne Twister algorithm and try implementing it yourself. Good luck.
Code:#include <stdio.h> void J(char*a){int f,i=0,c='1';for(;a[i]!='0';++i)if(i==81){ puts(a);return;}for(;c<='9';++c){for(f=0;f<9;++f)if(a[i-i%27+i%9 /3*3+f/3*9+f%3]==c||a[i%9+f*9]==c||a[i-i%9+f]==c)goto e;a[i]=c;J(a);a[i] ='0';e:;}}int main(int c,char**v){int t=0;if(c>1){for(;v[1][ t];++t);if(t==81){J(v[1]);return 0;}}puts("sudoku [0-9]{81}");return 1;}
