C++ generating random numbers-1

Question

int main() 
{ 
  srand((unsigned)time(0)); 
  int random_integer; 
  int lowest=0, highest=10; 
  int range=(highest-lowest)+1; 
  for(int index=0; index<20; index++){ 
    random_integer = (rand() % range) + lowest/(RAND_MAX + 1.0);
    cout << random_integer << endl; 
  } 
}

I am getting the output from 0 to 10, 11 numbers, but I don't want to get number 10, just numbers 0 to 9, that means 10 random numbers, what should I do?

change `highest=10` to `highest=9` ? i wouldnt change the code any other way since your variables give the impression that it should give "highest" number of 10... which wont work anymore if you follow Alexander's advice. — Rookie, Mar 01 '12 at 11:48
possible duplicate of [Generating random integer from a range](http://stackoverflow.com/questions/5008804/generating-random-integer-from-a-range) — mmmmmm, Mar 01 '12 at 11:49
@Alexander, it works perfectly, but i wanna know what that +1 means for the code there... could u please explain it. actual problem — visanio_learner, Mar 01 '12 at 11:52

score 3 · Accepted Answer · edited May 23 '17 at 12:29

3

Modulo operation x % c; returns the remainder of division of number x by c. If you do x % 10 then there are 10 possible return values: 0 1 2 3 4 5 6 7 8 9.

Note that generating random numbers by using rand() with % produces skewed results and those numbers are not uniformly distributed. Here's the simple C-style function that generates random number from the interval from min to max, inclusive:

int irand(int min, int max) {
    return ((double)rand() / ((double)RAND_MAX + 1.0)) * (max - min + 1) + min;
}

Note, that numbers generated by this functions are uniformly distributed:

int occurences[8] = {0};

srand(time(0));
for (int i = 0; i < 100000; ++i)
    ++occurences[irand(1,7)];

for (int i = 1; i <= 7; ++i)
    cout << occurences[i] << ' ';

output: 14253 14481 14210 14029 14289 14503 14235

Also have a look at:
Generate a random number within range?
Generate random numbers uniformly over an entire range
What is the best way to generate random numbers in C++?

edited May 23 '17 at 12:29

Community

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answered Mar 01 '12 at 11:49

LihO

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okay, but what you're expecting to get, is it 8 random numbers or just 7... because my question is all about the count of numbers that i get... i should only get 10 numbers from lowest being 0 and highest being 10... – visanio_learner Mar 01 '12 at 11:55
1

@visanio_learner: If you call my function like this: `irand(0,3)`, there are 4 possible return values: `0, 1, 2, 3`. Hope it's clear now ;) – LihO Mar 01 '12 at 11:58
@visanio_learner: Thank you. But someone dowvoted it and I'd like to know the reason. – LihO Mar 01 '12 at 12:54
@visanio_learner: I am not asking you. I just hope someone will read my comment and write the reason he downvoted... – LihO Mar 01 '12 at 12:59
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/8393/discussion-between-visanio-learner-and-liho) – visanio_learner Mar 01 '12 at 12:59

score 0 · Answer 2 · answered Mar 01 '12 at 11:48

0

It appears that you need to fully understand, then modify this line

random_integer = (rand() % range) + lowest/(RAND_MAX + 1.0);

answered Mar 01 '12 at 11:48

dklt

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score 0 · Answer 3 · answered Mar 01 '12 at 11:48

0

rand() % 10 normally does the trick for me.. (unless I'm missing something)

answered Mar 01 '12 at 11:48

Nim

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score 0 · Answer 4 · answered Mar 01 '12 at 11:59

int main() 
{ 
  srand((unsigned)time(0)); 
  int random_integer; 
  int lowest=0, highest=9; 
  int range=(highest-lowest)+1; 
  for(int index=0; index<20; index++){ 
    random_integer = (rand() % range) + lowest;
    cout << random_integer << endl; 
  } 
}

score 0 · Answer 5 · edited May 23 '17 at 12:29

0

this type of questions have been answered n number of times.

have a look at this

edited May 23 '17 at 12:29

Community

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answered Mar 01 '12 at 12:00

Rohit Vipin Mathews

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C++ generating random numbers-1

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