Equally distributed probability in C

I have a program that runs over 1000000 iterations to simulate server load. Arrival rate of requests is a variable. For example if arrival rate is 2: This means at every 2 iterations, there should be 1 request incoming which would generate "around" 500,000 requests at the end of simulation and so on. I can not do this just by introducing a new request at each nth interval depending on the arrival rate. There must be a factor of luck involved.

#include<stdio.h>
#include<time.h>
#include <stdlib.h>

//random number generator method
int random_number(int min_num, int max_num){
  int result=0,low_num=0,hi_num=0;

  if(min_num<max_num){
    low_num=min_num;
    hi_num=max_num+1; // this is done to include max_num in output.
  }else{
    low_num=max_num+1;// this is done to include max_num in output.
    hi_num=min_num;
  }
  result = (rand()%(hi_num-low_num))+low_num;
  return result;
}

int main(){
  srand(time(NULL));
  unsigned int arrivalRate = 2;
  unsigned int noOfRequests = 0;
  unsigned int timer;
  for(timer = 0; timer < 1000000; timer++){
    //gives a random number between 0 and arrival rate
    int x = random_number(0, arrivalRate);
    //there is a new request
    if(x <= 1){
      noOfRequests++;
    }    
  }
  printf("No of requests: %d", noOfRequests);
}

So, if I run this code with arrivalRate 2, it generates around 600,000 requests which should be only around 500,000 (+-1000 is tolerable) requests. How can I improve my code to generate more reasonable results, it is producing way too much than expected.

The result of the random function is uniformly distributed between 0 and 2. Which means the output is either 0, 1, or 2 with 33% probability each. You are testing for <= 1, which means you have a 67% probability of accepting the request, which is around 666K per million.

To solve your problem, you need to exclude the lower bound from the interval, change the computation of result to:

result = (rand()%(hi_num-low_num+1))+low_num;

Or you might want to exclude the upper bound instead, depending on what you need. Your statement "This means at every 2 iterations, there should be 1 request incoming" is not consistent with randomly picking 2 numbers out of a set of 3.