Why isn't this number random? - c

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.

Answer 3

Because the pseudo-random number generator used by rand is always initialized with the same seed.
In order to initialize it with a different seed, you can use the srand function, and initialize it as, say, srand(time(NULL)).

Answer 4

Because 83 is a random number, isn't it ?
More seriously, it is useful to have programs providing a repeatable behavior so by default, rand always returns the same sequence of numbers if you don't change the seed.

Answer 5

Seed the random number generator by including <time.h> and calling srand(time(0)); (edited thanks to my commenters)

Answer 6

You can not generate a random number which is truly random until and unless your random number generator has access to a truly random physical phenomenon as quoted earlier by peter. But for a general use you can use C's standard library functions for generating random numbers. Here is a sample code for generating random number between two limits(max and min):
#include<stdio.h>
#include<stdlib.h>
#define MIN 1
#define MAX 5
#define QUANTITY 5
int main()
{
int i;
//stores the time in seconds
time_t seconds;
//getting the system time
time(&seconds);
//initializing the random generator with system time
//as the seed value
srand((long)seconds);
for(i = 0; i < QUANTITY; i++)
{
printf("%f\t",((float)rand())/RAND_MAX*(MAX-MIN)+MIN);
}
printf("\n");
return 0;
}