Why Doesn't This Work??!!

thanks to Michael Ashley...

Code:

 
// An example showing how to generate random floating
// point numbers between 0 and 1.

// Michael Ashley / UNSW / 02-Apr-2003

#include <sys/time.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

int main(void) {
    struct timeval t;
	// Note that the structure timeval is defined in <sys/time.h> as {int t.tv_sec int t.tv_usec}
	// Here t.tv_sec is the time in seconds and 
	// t.tv_usec is the fractional part of the time in microseconds

    int i;

    // Obtain the time of day, to microsecond resolution.

    assert(0 == gettimeofday(&t, NULL)); 

    printf("The time is %ld.%06ld seconds since the Unix epoch\n",
	   t.tv_sec, t.tv_usec);

    // Use the number of microseconds as the seed for the system
    // random number generator.

    srandom(t.tv_usec);
  
    // Generate and print ten random integers between 0 and RAND_MAX.
    
    for (i = 0; i < 10; i++) {
        printf("%ld\n", random());
    }

    // Generate and print ten random numbers between 0 and 1.0.
    
    for (i = 0; i < 10; i++) {
        printf("%.15f\n", random()/((double) RAND_MAX));
    }

    return 0;
}

I proclaim this post, vague post of the week.

Anyway, it doesn't work because whatever half-assed version of <sys/time.h> you have doesn't have the functions used in this program. Most of them are not required by ISO sys/time.h as I understand it. That's fine because you can very easily fix this. If you include <time.h>, assuming <sys/time.h> doesn't already include it, you can replace all the functions with more standard ones.

Code:

for (i = 0; i < 10; i++) {
        printf("%.15f\n", random()/((double) RAND_MAX));
    }

should be

Code:

for (i = 0; i < 10; i++) {
        printf("%f\n", ((double)rand() / ((double)(RAND_MAX)+(double)(1)) ));
    }

a sample code which gnerated randonm number from [0,1] and [0,1000] floating point numbers

Code:

#include<stdio.h>
#include<stdlib.h>
#include<time.h>

int main()
{
    int i;
    double  X;
    
    srand(time(0));
    for(i=0;i<10;i++)
    {
        
        X = ((double)rand() / ((double)(RAND_MAX)+(double)(1)) );
        printf("%f \t %f\n",X,X*1000);
        
    }
    getchar();
    return 0;
}

/*my ouput
0.009277         9.277344
0.624451         624.450684
0.529999         529.998779
0.419037         419.036865
0.858154         858.154297
0.952148         952.148438
0.746246         746.246338
0.705444         705.444336
0.593781         593.780518
0.759460         759.460449
*/

ssharish2005

Originally Posted by ssharish2005

a sample code which gnerated randonm number from [0,1] and [0,1000] floating point numbers

Code:

#include<stdio.h>
#include<stdlib.h>
#include<time.h>

int main()
{
    int i;
    double  X;
    
    srand(time(0));
    for(i=0;i<10;i++)
    {
        
        X = ((double)rand() / ((double)(RAND_MAX)+(double)(1)) );
        printf("%f \t %f\n",X,X*1000);
        
    }
    getchar();
    return 0;
}

/*my ouput
0.009277         9.277344
0.624451         624.450684
0.529999         529.998779
0.419037         419.036865
0.858154         858.154297
0.952148         952.148438
0.746246         746.246338
0.705444         705.444336
0.593781         593.780518
0.759460         759.460449
*/

ssharish2005

Uh i see,

*but what should i do to confine the generated numbers to a range of say [0, 0] to [(Pi/2), 1]?

*Also, what should i change to produce 1000 random numbers instead of 10?

>*Also, what should i change to produce 1000 random numbers instead of 10?
to get 1000 change the for loop conition

>*but what should i do to confine the generated numbers to a range of say [0, 0] to [(Pi/2), 1]?
u got to mul the randon generated number (from the rand i.e X) by PI/2 instead ....

ssharish2005