Question

I wish to generate random numbers between 0 and 1. (Obviously, this has application elsewhere.)

My test code:

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

int main() {
double uR;
srand(1);
for(int i=0;i<5;i++){
    uR = rand()/(RAND_MAX+1.000);
    printf("%d \n", uR);
    }
}

And here’s the output after the code is compiled with GCC:

gcc -ansi -std=c99 -o rand randtest.c
./rand
0 
-251658240 
910163968 
352321536 
-528482304

Upon inspection, it turns out that casting the integer RAND_MAX to a double has the effect of changing its value from 2147483647 to -4194304. This occurs regardless of the method used to change RAND_MAX to type double; so far, I’ve tried (double)RAND_MAX and double max = RAND_MAX as well.

Why does the number’s value change? How can I stop that from happening?

Answer 1

You can’t print a double with %d. If you use %f, it works just fine.