Question

I have the following C++ code that tried to generate a random number. The idea is we given some rate ‘x’ and number of runs; we hope it would generate the number as many as (x * number of runs times).

#include <iostream>       #include <vector> #include <fstream> #include <sstream>        #include <time.h>         using namespace std;        int main  () {      // Initialize Random Seed      srand (time(NULL));      string line;     double SubsRate = 0.003;       double nofRuns   = 1000000;      for (unsigned i=0; i < nofRuns ; i++) {          int toSub = rand() % 1000 + 1;          if (toSub == (SubsRate * 1000)) {          cout << toSub << ' Sub'  << endl;          }      }     return 0; } 

Hence if we run the code above K times with this command:

$ a=0 ; while test $a -lt 10 ; do ./MyCode | wc -l ; a=`expr $a + 1` ; done 

We expect it to generate number ‘3’ as many as ~3000 times in 1M runs. But some how my code above my code above only generate number ‘3’ as many as 900 ~ 1000 times.

How can I improve on my code above?

Answer 1

In other words, you are checking that the result == 3, not that the result is <= 3.

3 will only happen, one in 1000 times, but <= 3 will happen at the rate you want.