Question

I have a simple integer vector, with only 4 values. I want to loop through the vector, assigning either 0 or 1 to each value. I want it to be random to the point that its different every time.

I thought the following would suffice:

  for (int i = 0; i < (int)numberVect.size(); i++)
  {
      numberVect[i] = rand() % 2;
  }

However, what I found was that every time I would close and re-open the program, the exact same values would be assigned.

So the first time through it would be 1,0,0,0, then if I ran the loop again without closing the program it would be 0,1,0,1. which seems perfect.

HOWEVER, after closing the program and restarting it up again, I would find the first sequence would again be 1,0,0,0 and the second would again be 0,1,0,1.

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Also I have a second question in relation to this problem:

Can you suggest a way to make sure that AT LEAST one of the values in the vector is a 1? while still allowing the random generation to work seamlessly?

Thanks a lot and I hope you guys can help 😀

Answer 1

You need to seed the random generator, before using it. For that you need srand()

I usually do that with passing current time to srand() as:

#include <time.h>

srand(time(NULL)); //seeding!

//now use
int whatever = rand();

Now everytime, you run this code you’ll get different random sequence,even if there is one second of difference between two consecutive runs.