C++ random function return same numbers

Question

I'm trying to get random numbers on range from 0 to 3. Using such code:

#include <cstdlib>
int index = rand() % 3;

But always getting the same results: 1 1 0 1.

What I'm doing wrong? Always the same numbers. Results should change their values after each compilation or during runtime?

score 6 · Accepted Answer · answered Feb 15 '13 at 18:30

6

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#include <ctime>
srand(time(NULL))

at the start of your program.

This will generate a new seed everytime you run your program based on the current time.

answered Feb 15 '13 at 18:30

http://www.kodyaz.com/images/pics/random-number-generator-dilbert-comic.jpg – user1511417 Feb 16 '13 at 15:41

juanchopanza · Answer 2 · 2013-02-15T23:50:22.777

Results should change their values after each compilation or during runtime?

Actually, no, the results are supposed to be the same for a given seed, and if you do not set the seed explicitly with srand(), then the results will be the same each time you run. To get different results each time, you should set the seed using something derived from something not completely deterministic, like the time (not deterministic in the sense that you don't know the exact time at the moment it gets used to set the seed).

C++ random function return same numbers

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