C：从 int 转换为 float 或 double 时出错

Question

I'm trying to generate a random number between 1 and 0 for a school project. Several places say this should be done using rand() and casting to float. Something like the following:

float x = ((float)rand()/(float)(RAND_MAX)) * a;

However, I discovered that whenever I cast from int to float the number is incorrect. This issue is causing me to get incorrect answers using the code above

Code:

int rotlat = rand() % 1000;
double newrot = (double) rotlat;
printf("rotational latency: %d\n", rotlat);
printf("new rotational latency: %d\n", newrot);

Output:

rotational latency: 533
new rotational latency: -1841876320

rotational latency: 279
new rotational latency: -1841876320

rotational latency: 148
new rotational latency: -1841876320

rotational latency: 167
new rotational latency: -1841876320

Answer 1

Try:

printf("new rotational latency: %g\n", newrot); //%g

The %d directive is for decimal integers, not doubles.