C random number

Question

This is my code

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


 main()
 {
    int r = rand() % 20;
    printf("%d", r);
 }

I want to get a random number 19 and below, but it just gives me 1 every time I compile and run it. Can someone show me what I am doing wrong?

You need to seed the random number generator, look up `srand()`. `main()` returns an `int`, by the way. — Crowman, Sep 21 '13 at 04:32
@samir: Look at any one of the numerous "related" questions attached to this very question. — Crowman, Sep 21 '13 at 04:35
You might want to try this XKCD's solution: http://xkcd.com/221/ (Sorry, I couldn't control!!) — Swanand, Sep 21 '13 at 11:59

score 1 · Accepted Answer · edited May 23 '17 at 11:58

1

Try

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


 int main()
 {
    srand(time(NULL));
    int r = rand() % 20;
    printf("%d", r);
 }

Note: Using the % is not a great way to get an even distribution.
See: Recommended way to initialize srand? for more info.

edited May 23 '17 at 11:58

Community

answered Sep 21 '13 at 04:34

Martin York

This is hardly any better. It will print the same number many times in a row if you run it rapidly. – R.. GitHub STOP HELPING ICE Sep 21 '13 at 05:20
@R..: I think you will find I already covered that situation in the link. – Martin York Sep 21 '13 at 06:06

score 0 · Answer 2 · answered Sep 21 '13 at 04:33

0

Read up about seeding the random number generator - i.e. http://linux.die.net/man/3/srand

answered Sep 21 '13 at 04:33

Ed Heal

score 0 · Answer 3 · answered Sep 21 '13 at 07:08

0

If you are using Turbo C++ 4.5 then put a

randomize();

before

int r=rand()%20;

It will also give your desired result.

answered Sep 21 '13 at 07:08

user2100721

3 Answers3