Does stdlib's rand() always give the same sequence?

Question

I quite like being able to generate the same set of pseudo-random data repeatedly, especially with tweaking experimental code. Through observation I would say that ran

Answer 1

If you are in a UNIX/Linux enviroment you can see the drand48() and srand48() at your man pages if you are not you can see online manuals for the C Language. The prototypes can be found at /usr/include/stdlib.h . The first one use the Linear Congruential Method that is frequently used in Simulations.

If you provide the same seed to srand48() i.e. srand48(2) and then put the dran48() in a for loop then the sequence will be the same every time. i.e.

include stdio.h
include stdlib.h
double drand48();
int main(void){
    int i;
    double rn;
    srand48(2);
    for(i=0; i<10; i++){
        randNum = drand48();
        printf("%.6l\n", randNum);
        return 0;
}