Demonstrate the dangers of calling rand() without calling srand().

test_rand.c

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

/*
 *  Require C99
 */

#if __STDC_VERSION__ < 199901L
#error C99 Required
#endif

int main(int argc, char ** argv){
	/*
	In all references I have checked, the default seed for the PRNG
	in C is the number 1.
	*/
	printf("Unseeded\n");
	for(int i = 0; i < 5; i++){
		printf("\trand[%d] = %d\n", i, rand());
	}
	/*
	Common practice is to seed the PRNG with the current time. This
	ensures that the numbers generated are different for each program
	execution, assuming each execution occurs at least one second apart.
	*/
	srand(time(NULL));
	printf("\nSeeded with current time\n");
        for(int i = 0; i < 5; i++){
                printf("\trand[%d] = %d\n", i, rand());
        }
	/*
	Here the PRNG is seeded with the number 1, showing that the
	sequence generated is identical to that generated befiore srand was
	called.
	*/
	srand(1);
        printf("\nSeeded with 1\n");
        for(int i = 0; i < 5; i++){
                printf("\trand[%d] = %d\n", i, rand());
        }

}