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

thx. the reason i was adding was to avoid '0' as the random number in my code. rand()+rand() was the quick dirty solution which readily came to my mind

It sounds like an XY problem to me, in which in order to not get a 0 from rand(), you call rand() two times, doing the program slower, with a new setback and the possibility of getting a 0 is still there.

Another solution is using uniform_int_distribution, which creates a random and uniformly distributed number in the defined interval:

https://wandbox.org/permlink/QKIHG4ghwJf1b7ZN

#include 
#include 
#include 
 
int main()
{
    const int MAX_VALUE=50;
    const int MIN_VALUE=1;
    std::random_device rd;
    std::mt19937 gen(rd());
    std::uniform_int_distribution<> distrib(MIN_VALUE, MAX_VALUE);
    std::array weight={0};

    for(int i=0; i<50000; i++) {
        weight[distrib(gen)-MIN_VALUE]++;
    }
    
    for(int i=0;i<(int)weight.size();i++) {
        std::cout << "value: " << MIN_VALUE+i << " times: " << weight[i] << std::endl; 
    }
}