Generate a Random Number between 1 and N-1

Question

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How to generate a random number from within a range - C

How would you generate a random number between 1 and N-1 where N is a number the user punches in?

So far, my code is:

#include <stdio.h>
#include <stdlib.h>
int main()
{
    int number = 0; //number variable
    printf("This program will ask you for a number, an integer, and will print out a    random number from the range of your number 1, to N-1.");//output that explains the program's purpose and use to the user.
    //gets the input
    fgets(buffer, sizeof(buffer), stdin);
    sscanf(buffer, "%d", &number); //gets the input and stores it into variable number

    return (0);

}

tip: look for a function that return a random number and use a modulus operator — Bartlomiej Lewandowski, Jan 18 '13 at 17:08

score 1 · Answer 1 · answered Jan 18 '13 at 17:09

1

Here is the link to the referece for random.

http://www.cplusplus.com/reference/cstdlib/rand/

you can use

num= rand() % n + 1;

answered Jan 18 '13 at 17:09

Luis Tellez

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simple and clean. I like it – Andreas Grapentin Jan 18 '13 at 18:36

score 1 · Answer 2 · edited Jan 21 '13 at 09:17

1

Depending on how "random" you want your numbers to be, you can use rand() function from the standard libc. This function will generate numbers between 0 and RAND_MAX. You can then get the result in the good range by using a modulo operation.

Note that this generator (a LCG) is neither suitable for cryptographic applications nor scientific applications.

If you want more suitable generators, have a look at generators such as Mersenne Twister (still not cryptosecure though).

edited Jan 21 '13 at 09:17

jopasserat

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answered Jan 18 '13 at 17:11

Heis Spiter

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`NOT suitable for cryptographic applications nor scientific applications` From the looks of the question and context I don't think we have to worry about that. ;) – Mike Jan 18 '13 at 17:31
Sure, but that's just in case someone would use this answer for something else :-) – Heis Spiter Jan 18 '13 at 17:43

score 1 · Accepted Answer · answered Jan 18 '13 at 17:12

1

Try something like this:-

unsigned int
randomr(unsigned int min, unsigned int max)
{
       double x= (double)rand()/RAND_MAX;

       return (max - min +1)*x+ min;
}

Check out this link:- http://c-faq.com/lib/randrange.html

answered Jan 18 '13 at 17:12

Rahul Tripathi

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score 0 · Answer 4 · answered Jan 18 '13 at 17:08

0

You need to look at rand. Bit of maths and you have a solution.

answered Jan 18 '13 at 17:08

Ed Heal

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Generate a Random Number between 1 and N-1

4 Answers4