Why does rand() + rand() produce negative numbers?

Question

I observed that rand() library function when it is called just once within a loop, it almost always produces positive numbers.

for (i = 0; i <         


        

Answer 1

Basically rand() produce numbers between 0 and RAND_MAX, and 2 RAND_MAX > INT_MAX in your case.

You can modulus with the max value of your data-type to prevent overflow. This ofcourse will disrupt the distribution of the random numbers, but rand is just a way to get quick random numbers.

#include 
#include 

int main(void)
{
    int i=0;

    for (i=0; i<100; i++)
        printf(" %d : %d \n", rand(), ((rand() % (INT_MAX/2))+(rand() % (INT_MAX/2))));

    for (i=0; i<100; i++)
        printf(" %d : %ld \n", rand(), ((rand() % (LONG_MAX/2))+(rand() % (LONG_MAX/2))));

    return 0;
}