Mick - 6 months ago 74

C++ Question

I am an experienced C programmer that is occasionally forced to use a little bit of C++.

I need to generate random numbers from a normal distribution with a variety of means and variances. If I had a C function that did this called

`normal(float mean, float var)`

`int i;`

float sample;

for(i = 0;i < 1000;i++)

{

sample = normal(mean[i],variance[i]);

do_something_with_this_value(sample);

}

Note that there is a different mean and variance for each value of i.

C does not contain a function called normal, but C++ does, well actually its called std::normal_distribution. Unfortunately my C++ is not good enough to understand the syntax in the documentation. Can anyone tell me how to achieve the functionality of my C code but using std::normal_distribution.

Answer

`std::normal_distribution`

isn't function but templated class

you can use it like this:

```
#include <random>
int main(int, char**)
{
// random device class instance, source of 'true' randomness for initializing random seed
std::random_device rd;
// Mersenne twister PRNG, initialized with seed from previous random device instance
std::mt19937 gen(rd());
int i;
float sample;
for(i = 0; i < 1000; ++i)
{
// instance of class std::normal_distribution with specific mean and stddev
std::normal_distribution<float> d(mean[i], variance[i]);
// get random number with normal distribution using gen as random source
sample = d(gen);
// profit
do_something_with_this_value(sample);
}
return 0;
}
```