Why does this code always generate zero when I want to generate random numbers? How can I fix the problem?

Question

#include <iostream>
#include<stdio.h> 
#include<stdlib.h> 
#include<time.h> 
 
using namespace std;
 
class mRND
{
    public:
        void seed()
        {
            srand(time(0)); 
            _seed = rand();
        }
 
    protected:
        mRND() : _seed(), _a(), _c(), _m(2147483648)
        {
        }
        int rnd()
        {
            return (_seed = (_a * _seed + _c) % _m);
        }
 
        int _a, _c;
        unsigned int _m, _seed;
};

int main() {
    mRND r;
    for(int i=0;i<100;i++)
    cout<< r.rnd()<<endl;
    
    return 0;  
}

You never give _seed, _a or _c any values, so it just keeps using 0 and 0*0+0 = 0. — Delta_G, Aug 08 '20 at 23:28

score 4 · Accepted Answer · answered Aug 08 '20 at 23:29

4

Your problem is here:

return (_seed = (_a * _seed + _c) % _m);

_a is 0 so the returned value is 0 and it never changes (since _a is always 0).

answered Aug 08 '20 at 23:29

Object object

1,939
10
19

score -8 · Answer 2 · answered Aug 08 '20 at 23:27

-8

Try setting time as "NULL" rather than zero. Zero, in this case, would likely mean midnight on January 1st, 1970. If this is the case, you would keep getting the random seed that occurs with that time.

answered Aug 08 '20 at 23:27

mpekim

29
1
1
6

Why does this code always generate zero when I want to generate random numbers? How can I fix the problem?

2 Answers2