Generating a random, uniformly distributed real number in C [duplicate] - c

Question

This question already has answers here:
Generate random double number in range [0, 1] in C
(2 answers)
Closed 2 years ago.
I would like to generate a random, real number in the interval [0,1].
I would like to set a pointer, say n, for the number so whenever I stated n, it will be referred to the random generated number.
I have searched on StackOverflow and on Google, but most of them are for C++ or for integers.
I have tried this code suggested to me in the answers:
#include <stdio.h>
#include <stdlib.h>
int main()
{
double n;
double get_random() { return (double)rand() / (double)RAND_MAX; }
n = get_random();
printf("%f", n);
return 0;
}
However, I can only get a value 0.00000000.
How could I fix my program?

Answer 1

You can use:
#include <time.h>
srand(time(NULL)); // randomize seed
double get_random() { return (double)rand() / (double)RAND_MAX; }
n = get_random();
srand() sets the seed which is used by rand to generate pseudo-random numbers. If you don't call srand before your first call to rand, it's as if you had called srand(1) (serves as a default).
If you want to exclude [1] use:
(double)rand() / (double)((unsigned)RAND_MAX + 1);
Full solution:
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
double get_random() { return ((double)rand() / (double)RAND_MAX); }
int main()
{
double n = 0;
srand(time(NULL)); // randomize seed
n = get_random(); // call the function to get a different value of n every time
printf("%f\n", n); // print your number
return 0;
}
Every time you run it you will get a different number for n.

Answer 2

This shows how to get random real numbers in the range 0..1 but please note that they are not uniformly distributed. There are only (RAND_MAX+1) discrete values.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main(void) {
int i;
double n;
srand((unsigned)time(NULL)); // seed the random num generator ONCE only
for(i = 0; i < 3; i++) { // get 3 random numbers
n = (double)rand() / RAND_MAX; // in the range 0 ... 1
printf("%f\n", n); // use correct format specifier for the var
}
return 0;
}
My program output:
0.622608
0.814081
0.878689