Thread: Random Numbers

Is there anyway at all of generating a random number?

The function rand() just generates the name numbers in the same order every single time. For example,

Code:

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

int main()
{
    int n;
    int x;
    for (x=0;x<30;x++)
    {
        n=rand();
        printf("%d", n);
        getchar();
    }
    return 0;
}

Will ALWAYS output:

41
18467
6334
26500
19169
15724
etc...

I noticed a tutorial for it, but like basically everything else it is C++*. So is it actually possible in C?

*Note that I'm not complaining about this.

Code:

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

int main()
{
    int n;
    int x;
    srand(time(NULL));
    for (x=0;x<30;x++)
    {
        n=rand();
        printf("%d", n);
        getchar();
    }
    return 0;
}

Perfect!

Now how do I limit it? Basically I want to randomly generate a number between 0 and 9.

Originally Posted by mortalc

Perfect!

Now how do I limit it? Basically I want to randomly generate a number between 0 and 9.

Just use ... n = rand() % 10; ... the number will be 0 to 9 inclusive.

So say if I use rand() %11; the highest will be ten.

Try using

Code:

Include time.h
Then in function
srand(time(NULL));
int x=rand()%11;
// This will provide you unique random numbers most of the times....

This is weird. Here is the main bit of my code:

Code:

    int sudoku[8][8];
    int i;
    int a;
    int b;
    srand(time(NULL));
    for(a=0;a<9;a++)
    {
        for(b=0;b<9;b++)
        {
            i=rand() %20;
            if (i<10 && i!=0)
            {
                sudoku[a][b]=i;
            }
               printf("[%2d]", sudoku);
        }
    }

It writes [2686476][2686476] etc... A lot of times. I don't know if it is the required 81 or not.
What I want is something like:

[][][][2][6][][8] etc. in 9 rows of 9.

If it is not between 1 and 9, I don't want it to have a value; it is equivalent of the empty box in your sudoku puzzle.

Aha-ha! I should have written

Code:

printf("[%2d]", sudoku[a][b]);

If you want empty boxes... that is, a certain condition without writing to the array you need to intialize it to these values before beginning... otherwise the array is filled with unknown values that may interfere in the correct solution of the puzzle.

Code:

sudoku[8][8] = {0};

I am now using this code to create it:

Code:

int sudoku[8][8] = {0};
    int i;
    int a;
    int b;
    srand(time(NULL));
    for(a=0;a<9;a++)
    {
        for(b=0;b<9;b++)
        {
            i=rand() %20;
            if (i<10 && i!=0)
            {
                sudoku[a][b]=i;
            }
               printf("[%d]", sudoku[a][b]);
        }
        printf("\n");
    }

Unfortunately there are a few problems. It will usually create a 9x9, but sometimes it is more of a 20x9. Also, sometimes one or two of the numbers will be absurdly big.