random numbers limit

I wrote this code it generates ramdom numbers but the problem is that it keeps gererating the same random numbers all the time how do i make it so the code generates different ramdom numbers all the time. Plus I would like to have the random numbers from -0.5 to 2.5
can some one point me to the right direction.

Code:

---


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

int main()
{
       
 int i,a;
 
for (i = 0; i < 10; i++)
    {
        a=rand();       
        printf("%d\n",a);
    }
 
    return 0;
}

---

You have to seed it.

http://www.cplusplus.com/ref/cstdlib/srand.html

Code:

---

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

int main()
{
       
 int i,a;
 srand(time(0));
for (i = 0; i < 10; i++)
    {
        a=rand()%100;  // ranon number with in 100       
        printf("%d\n",a);
    }
  getchar();
    return 0;
}
/*myoutput
87
79
3
63
68
70
2
15
86
94
*/

---

ssharish2005

To further the point, time.h is not needed at all in your current code. The reason you'll find it included frequently when you see rand used, is because people use time to seed srand. If you aren't seeding with time, then you don't need to include it's header.


Quzah.

Thanks for the code it's now generating time dependant random numbers but I want to limit it betbeen -0.5 and 2.5 what modifications must be made to the code to limit it.

Code:

---

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

int main()
{

    int i,a;

    /* Set evil seed (initial seed) */
    srand( (unsigned)time( NULL ) );

    for (i = 0; i < 12; i++)
    {
        a=rand()%100;       
        printf("%d\n",a);
    }
 
    return 0;
}

---

upper limit can be set like this

Code:

---

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

int main()
{

    float i,a;
        float temp;
    /* Set evil seed (initial seed) */
    srand( (unsigned)time( NULL ) );

    for (i = 0; i < 12; i++)
    {
        a=rand()%100;
                temp=a/39.6f;
        printf("%f\n",temp);
    }
       
 
    return 0;
}

---

Code:

---

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

int main()
{

    float i,a;
    srand( time( 0 ) );

    for (i = 0; i < 12; i++)
    {
        a=rand()%30;  //now the range is 0 - 29
        a=a/10-0.5;    //a/10---0 to 2.9xxx subtracting 0.5 from it
        printf("%1.1f\n",a);
    }

    return 0;
}

---

1 Possible soln would be.

I seen to have over come the problem of generationg time dependant random numbers abd I also midified the code to give me an output in my desired range but I can'nt seem to store it in an array I would find it very helpful if someone cam point me to the right direction and tell me where I went wrong.

Code:

---


#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define x 10

int main()
{

    float i,a;
    float s[x];
    srand( time( 0 ) );

    for (i = 0; i <=10; i++)
    {
        a=rand()%26; 
        a=a/11;   
        s[i]=a;
        scanf("%1.1f",&s[i]);
        printf("%1.1f\n",s[i]);
    }

    return 0;
}

---

it should be int i instead of float i

If you actually did a board search you'd find a massive amount of random number functions that take a range.

The basic way is this:
Take your upper bound and subtract your lower bound. This is now your range.
Get a number in the set of 0 to range
Add your lower limit
You now have a number between your lower limit and your upper limit.