Why do I always get the same sequence of random numbers with rand()?

Question

This is the first time I\'m trying random numbers with C (I miss C#). Here is my code:

int i, j = 0;
for(i = 0; i <= 10; i++) {
    j = rand();
    printf         


        

Answer 1

rand() returns pseudo-random numbers. It generates numbers based on a given algorithm. The starting point of that algorithm is always the same, so you'll see the same sequence generated for each invocation. This is handy when you need to verify the behavior and consistency of your program.

You can set the "seed" of the random generator with the srand function(only call srand once in a program) One common way to get different sequences from the rand() generator is to set the seed to the current time or the id of the process:

srand(time(NULL)); or srand(getpid()); at the start of the program.

Generating real randomness is very very hard for a computer, but for practical non-crypto related work, an algorithm that tries to evenly distribute the generated sequences works fine.