Why isn't this number random?

Question

For the following piece of code:

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

int main()
{
    int x;
    x = rand()%100;
    printf("The Random Number is: %i", x);

return 0;
}

It always seems to print the random number as 83. Why is this?

Answer 1

Most random number generators are repeatable. You need to seed the generator before using it which you typically do using the system time.

#include <time.h>
srand(time(NULL));

Answer 2

Obligatory XKCD reference:

As people have said, you need to seed the pseudo random number generator properly.

The trouble is, it still only generates pseudo random numbers. Most "true" random number generators require access to some physical phenomenon that is random in nature (for example, clock skews or temperature fluctuations).

Otherwise, the XKCD reference is not too far from the truth. Nor is Dilbert.