Random generator 0 1

Dedalus · 06-30-2009, 08:35 AM

Hi

I'd like to write a random number generator between 0 and1.
I'm doing like that:

Code:

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

int main(){
int b;
float r;

srand(time(NULL));

printf("%d",RAND_MAX);

for (b=11;b>0;b--){

        r=rand();

        printf("%f\n", r/RAND_MAX);

        }
return 0;
}

but i get this output:

Code:

21474836470.216477
0.471353
0.312465
0.644094
0.796645
0.112260
0.999378
0.374815
0.463826
0.021919
0.175329

why the first one is not normalized?

Thanks

D.

**laserlight** · 06-30-2009, 08:38 AM

You printed RAND_MAX without a newline, so you confused that and the very first pseudorandom number printed. Try:

Code:

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

int main(){
    int b;
    float r;

    srand(time(NULL));

    printf("%d\n", RAND_MAX);

    for (b=11;b>0;b--){
        r = rand();

        printf("%f\n", r/RAND_MAX);
    }
    return 0;
}

Dedalus · 06-30-2009, 08:42 AM

many thanks, I made an easy error.

D.

**laserlight** · 06-30-2009, 08:44 AM

By the way, the range you get is [0.0, 1.0], but [0.0, 1.0) is more commonly used, methinks. If you want the latter, you would have to say, add 1.0 to RAND_MAX in the divisor.

06-30-2009, 08:38 AM	#2
laserlight C++ Witch Join Date: Oct 2003 Location: Singapore Posts: 10,352	You printed RAND_MAX without a newline, so you confused that and the very first pseudorandom number printed. Try: Code: #include<stdio.h> #include <stdlib.h> #include <time.h> int main(){ int b; float r; srand(time(NULL)); printf("%d\n", RAND_MAX); for (b=11;b>0;b--){ r = rand(); printf("%f\n", r/RAND_MAX); } return 0; } __________________ C + C++ Compiler: MinGW port of GCC Build + Version Control System: SCons + Bazaar Look up a C/C++ Reference and learn How To Ask Questions The Smart Way
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06-30-2009, 08:42 AM	#3
Dedalus Registered User Join Date: Jun 2009 Posts: 31	many thanks, I made an easy error. D.
Dedalus is offline

06-30-2009, 08:44 AM	#4
laserlight C++ Witch Join Date: Oct 2003 Location: Singapore Posts: 10,352	By the way, the range you get is [0.0, 1.0], but [0.0, 1.0) is more commonly used, methinks. If you want the latter, you would have to say, add 1.0 to RAND_MAX in the divisor. __________________ C + C++ Compiler: MinGW port of GCC Build + Version Control System: SCons + Bazaar Look up a C/C++ Reference and learn How To Ask Questions The Smart Way
laserlight is online now

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