I need to generate random numbers between two specified numbers in a loop with a uniform distribution. I am using the random library of C++11.
My problem is that I keep getting the same number in the loop. It is required that the number generated on every loop pass be different. Code below:
#include <cstdlib>
#include <stdio.h>
#include <iostream>
#include <random>
using namespace std;
double randnum (double a, double b)
{
std::default_random_engine generator;
std::uniform_real_distribution<double> distribution (a,b);
double num=distribution(generator);
return num;
}
int main()
{
int np=100;
double umin =0;
double umax=0.5;
double u[np];
for (int i=0;i<np;i++)
{
u[i]=randnum(umin,umax);
cout<<u[i]<<endl;
}
}
Please help. Any advice on generating random number by any alternative means is welcome, but it must have a uniform distribution.
The random number engines in the Standard Library are pseudo-random, i.e. deterministic in how their internal state is initialized and mutated. This means that each function call will get a fresh new generator that will continue to give the same number over and over again.
Just make the generator a static function variable so that its state can evolve over different function calls.
#include <iostream>
#include <random>
using namespace std;
double randnum (double a, double b)
{
static std::default_random_engine generator;
std::uniform_real_distribution<double> distribution (a,b);
return distribution(generator);
}
int main()
{
const int np=100;
double umin =0;
double umax=0.5;
double u[np];
for (int i=0;i<np;i++)
{
u[i]=randnum(umin,umax);
cout<<u[i]<<endl;
}
}
Note, you will get the same sequence of numbers for each run of your compiled program. To get more random behavior across program invocations, you can use e.g. std::random_device.
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