Why does the following code fail?

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I am wondering why the following code fail. I thought it will generate a new number every time the random() function is called, albeit recursively. But it seems that the number remains stationary for a pretty long time before changing. Why is that the case? And how can I change it so that every time it is called, a new number will be generated?

Thanks a lot!

What I have tried:

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

int i=0;
int random();

int main(){
    random();
    return 0;
}

int random(){
    int a;
    i+=1;
    srand(time(NULL));
    a=rand()%20;
    printf("This is the %d th iteration\n",i);
    printf("random number generated is: %d\n",a);
    if(a<8)
        random();
}

Posted 20-Feb-17 11:21am

Member 13013165

Updated 20-Feb-17 12:03pm

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Comments

Afzaal Ahmad Zeeshan 20-Feb-17 17:29pm

You need to learn the basics of random in programming languages. The random numbers generated, are not random. There is a pattern in them.

Read more by Googling. I will not answer. So that you may learn it yourself.

2 solutions

Solution 2

try

C++

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

int i=0;
int random();

int main(){
    srand(time(NULL));
    random();
    return 0;
}

int random(){
    int a;
    i+=1;
    a=rand()%20;
    printf("This is the %d th iteration\n",i);
    printf("random number generated is: %d\n",a);
    if(a<8)
        random();
}

The problem is with srand(). the random number generator is not random, it is pseufo-random, it means that if you set the seed 2 times with same value, you will get the same 'random' sequence. And since your seed is a number of seconds, you get every time the same sequence.

Posted 20-Feb-17 12:03pm

Patrice T

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Graeme_Grant · Accepted Answer · 2017-02-20T11:28:00

Solution 1

Google is your friend ... you need to do some research and learn how to use the rand function properly... c rand number[^]

From the google search above: C library function - rand()[^]

C++

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

int main()
{
   int i, n;
   time_t t;
   
   n = 5;
   
   /* Intializes random number generator */
   srand((unsigned) time(&t));

   /* Print 5 random numbers from 0 to 19 */
   for( i = 0 ; i < n ; i++ ) 
   {
      printf("%d\n", rand() % 20);
   }
   
   return(0);
}

Posted 20-Feb-17 11:28am

Graeme_Grant

Updated 20-Feb-17 13:43pm

v3

Comments

Member 13013165 20-Feb-17 17:45pm

Hello, thanks for pointing me to google. I will try harder to find a solution first (which I tried previously but probably following the comments from Stack Overflow isn't the best source to understand the issue). As a side note, I must say I am quite discouraged from Stack Overflow. I asked 2 questions and got banned from asking any more questions. I hope I will feel more encouraged asking questions here. Thanks.