rand not applying correctly?

[binga30]

Hi I am trying to generate a random number between 1 - 100 using the example on this site. It works...sort of, except the number is never between my given range.

CODE:
srand(time(NULL));
distance = rand() % 100 + 1;

I always get numbers around 270-390. I have not set this anywhere.
When i tried to get a number between 200-250 i used:

srand(time(NULL));
distance = rand() % 250 + 200;

This gave numbers like 350-490.

What have I missed?

[Peter87]

srand(time(NULL));
distance = rand() % 100 + 1;
I always get numbers around 270-390.

This I don't understand.

srand(time(NULL));
distance = rand() % 250 + 200;
This gave numbers like 350-490.

rand() % 250 returns a value 0-249 so rand() % 250 + 200 should give you a value 200-449.

I think you better show some real code.

[binga30]

Thanks for your response. I am at work now so i dont have my project handy. Its a simple console app in vsc++ 2008 express edition.

Judging by the first lot of code, I should get a number between 1-100 right?

I dont, but then why dont i get a number between 200-250 with the second lot of code?

If i replace the 1 with 200, and 100 with 250 should it not produce a range of 200-250?

[long double main]

If you want a random number from a to b, it's
rand() % (b - a + 1) + a

So from 200-250, it's
rand() % 51 + 200

If you didn't get a number between 1 - 100 with
rand() % 100 + 1,
then check to make sure you didn't make a typo.

[binga30]

Heres my code:

//Golf game test
#include <iostream>
#include "time.h"
using namespace std;

int main (void) {
int firstshot, distance;

srand(time(NULL));
distance = rand() % 51 + 200;


//First hole
cout << "Hole 1: 554m : Par 5" << endl;
cout << "1. Driver, 2. 3 Wood, 3. Iron" << endl;
cin >> firstshot;
//If you chose driver you will be penalised
if(firstshot==1){
cout << "You landed in the rough!" << endl;

cout << distance << " meters to hole" << endl;
}
//If you chose 3 Wood or iron lucky you
else {
cout << "You landed in the fairway!" << endl;
}

cout << "1. 3 Wood, 2. Iron, 3. Wedge" << endl;

//pausing game so it doesnt quit
system("pause");
return 0;
}

Its still not giving numbers in the range i specify.

[Peter87]

distance is between 200-250. Isn't that what you want?

[binga30]

Yes but the output is not always between 200-250. With this code the first three attempts were 241, 389, 357.

Is there something wrong with my code?

Also when i had 100 + 1 in there i kept getting the same sort of range about 250-500.

Would just like to know if I have done something wrong?

[Peter87]

No the code is correct. Are you sure you have compiled the code and running the correct program?

[Zephilinox]

try this instead, it is my preferred method of generating a random number, although I've simplified the general structure of it for you.

//your includes

int randomize(int max = 99, int min = 1)
{
    // don't forget to seed once in main.
    max++;
    max -= min;
    return (rand() % max + min);
}

int main()
{
    //blah blah blah
    distance = randomize(250, 200);
    //blah blah blah
}

see if that works.

[binga30]

Ive just been rebuilding my file, and then debugging. Its only in the console, anything else I should do?

[Zephilinox]

what IDE are you using? Dev-C++ is out of date and may be the cause of the problem.

[binga30]

Microsoft VS C++ 2008 the free edition

[Zephilinox]

I don't know much about VS, but I do know 2008 isn't the latest version, see if the newer one fixes the problem, I believe it is 2010.

[binga30]

I may have too. I was recommended this version because it was free from MS. I may just start a new project and see if that fixes it first.
Thanks for your help

[long double main]

What do you get as output for this program?

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;

int main()
{
    srand(time(0));
    for (int i = 0; i < 10; ++i)
        cout << rand() % 51 + 200 << '\n';
    return 0;
}

[Zephilinox]

isn't the 2010 version also free? if you are looking for a good free compiler, I recommend Code::Blocks.

[binga30]

Ok ill admit im a total noob but something funny is up. Possibly my skills.

Long Double , I copied and pasted your code over my existing code, rebuilt the file and went to debug. I am still getting my golf info asking me for input. Which it again gave me 300 as the number.

Do I assume I need to compile the program another way?

[long double main]

Err, I meant to compile that program by itself (don't copy/paste it into anything) and tell me what you get as output.

For instance, with MSVC++ 2010, I get something like this:

216
204
208
230
211
224
226
223
234
234

[binga30]

Ok i put it in a new project and ran the debug.
Yes i got a range of numbers between 200-250.

Your formula is a little different to what I had, would you mind explaining what the ++i and the '\n' mean?

[Zephilinox]

++i just adds one to i, \n simply means end the line, so that you don't get all the numbers showing on a single line (at least until it wraps around the console window)