```
// evaluation of three simple random number generators
// Written in Turbo C, modified for Pelles C
// get Pelles C for free: http://smorgasbordet.com/pellesc/index.htm
// this C package comes with a great IDE
#include <stdio.h> // printf(), getchar(), puts()
// three different custom random number generators
int rand1(int lim);
int rand2(int lim);
int rand3(int lim);
int main(void)
{
int k, rnd1, rnd2, rnd3, sum1, sum2, sum3;
sum1 = sum2 = sum3 = 0;
puts("Random numbers between 1 and 44:\n");
printf("%15s%10s %10s %10s","Custom functions","rnd1()","rnd2()","rnd3()");
for (k = 0; k < 40; k++) {
rnd1 = rand1(44); // method one
rnd2 = rand2(44); // method two
rnd3 = rand3(44); // method three
printf("\n%25d %10d %10d",rnd1,rnd2,rnd3);
sum1 += rnd1;
sum2 += rnd2;
sum3 += rnd3;
}
printf("\n\n%15s%10d %10d %10d (ideal 22)\n",
" Average:",sum1/k,sum2/k,sum3/k);
getchar(); // wait
return 0;
}
//
// returns random integer from 1 to lim
//
int rand1(int lim)
{
static long a = 100001;
a = (a * 125) % 2796203;
return ((a % lim) + 1);
}
//
// returns random integer from 1 to lim (Gerhard's generator)
//
int rand2(int lim)
{
static long a = 1; // could be made the seed value
a = (a * 32719 + 3) % 32749;
return ((a % lim) + 1);
}
//
// returns random integer from 1 to lim (Bill's generator)
//
int rand3(int lim)
{
static long a = 3;
a = (((a * 214013L + 2531011L) >> 16) & 32767);
return ((a % lim) + 1);
}
```

0

To use the time as the seed is very simple.

Make sure you include the <ctime> header.

`#include <ctime>`

Then, inside ctime there is a function you can call like this:

`time(0);`

When you pass this method zero, it returns the time elapsed since January 1, 1970. This way you are guaranteed a differerent number each run time(if you run it less than 1 time per second).

Ok, so back to "how to make the time the seed" question. In these code examples replace the arbitrary number assigned to a with:

`static long a = long(time(0));`

Next, perform your random number generation using whichever method.

-1

It is one of the simplest logics, got it from a blog. in this logic you can limit the random numbers with that given modulus(%) operator inside the for loop,its just a copoy and paste from that blog, but any way check it out:

[

```
// random numbers generation in C++ using builtin functions
#include <iostream>
using namespace std;
#include <iomanip>
using std::setw;
#include <cstdlib> // contains function prototype for rand
int main()
{
// loop 20 times
for ( int counter = 1; counter <= 20; counter++ ) {
// pick random number from 1 to 6 and output it
cout << setw( 10 ) << ( 1 + rand() % 6 );
// if counter divisible by 5, begin new line of output
if ( counter % 5 == 0 )
cout << endl;
}
return 0; // indicates successful termination
} // end main
- See more at: http://www.programmingtunes.com/generation-of-random-numbers-c/#sthash.BTZoT5ot.dpuf
```

Two problems. One is that this thread is 8 years old! Two is that writing *good* random number generators is not a trivial undertaking, and thinking it is just shows your ignorance of the subject. Read this: http://www.phy.ornl.gov/csep/CSEP/RN/RN.html

From the document, 2 relevant quotes:

Anyone who considers arithmetical methods of producing random digits is, of course, in a state of sin. -- John von Neumann (1951)

Anyone who has not seen the above quotation in at least 100 places is probably not very old. -- D. V. Pryor (1993)

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