How to calculate the average of a set of random numbers including additional conditions in C?

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I'm trying to calculate the average of a set of random numbers (all of them between 0 and 1), considering if other conditions are fulfilled. That is, calculate the average of a list of random numbers for every value of a float "y" while it is less than 1. I also need to consider the number of iterations required to do it.

The following is the code I wrote so far:

What I have tried:

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

#define L 2
#define STEPS 10
#define ITERATIONS L*L

FILE *doc;

float mean(float sum, float counts){
   double mean = 0.0;
   mean = sum/counts;
   return mean;
}


int main(){
    doc = fopen("document.txt","w");
    double y=0.0;
    float r;
    float sum_r=0.0; 
    float mean_r=0.0;
    srand((unsigned)time(0));

        fprintf(doc,"y                   mean of r        iterations \n");
        printf("y                   mean of r        iterations \n");

  
     for(int iter = 0; iter < ITERATIONS; iter++){

        while(y<1){ 
        	sum_r = 0;
            for (int t = 0; t < STEPS; t++){
                    r = rand()/(float)RAND_MAX;
                    sum_r+=r;  
            }
                mean_r = mean(sum_r,(float)STEPS);
                 y = y + 1/((double)(STEPS*ITERATIONS));
                
                fprintf(doc," %lf          %f           %d\n",y,mean_r,ITERATIONS);
                printf(" %lf          %f           %d\n",y,mean_r,ITERATIONS);
        }   
       
    }   
    fclose(doc);
    return 0;
}

The problem is that I get averages above of 1, and it is incorrect. Also, I don't know exactly how to include the "ITERATIONS" since I get incorrect values for the average of those number every time.

Note:

What I need to obtain is something like:

for y=0.00
   calculate the average of:
        0.3545
        0.5678
        0.2346
           .
           .
           .
        0.6786

for y=0.01
   calculate the average of:
        0.7893
        0.1234
        0.3899
           .
           .
           .
        0.8726

for y=0.02
           .
           .
           .
           .

and so on only while "y" is less than 1 and considering the number of iterations.

Posted 21-Feb-23 17:15pm

Auyik

Updated 22-Feb-23 12:39pm

v6

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OriginalGriff · Answer 1 · 2023-02-21T18:43:00

Solution 1

That code doesn't compile:

C

fprintf(doc," %f          %f          %f    \n\n",y,mean_r,);

You have specified three "%f" parameters in the format string but provided two, and have an empty parameter at the end - you'll get an error for the ",)" part, and a problem when it tries to execute if you remove the ",".

Try resetting sum_r after each STEPS iteration.

The way I'd do it is to write a function which generated a set of random numbers and returned the average.
Then call that repeatedly for each value of y and print the result.

Posted 21-Feb-23 18:43pm

OriginalGriff

Comments

CPallini 22-Feb-23 2:13am

5.

Auyik 22-Feb-23 5:41am

Sorry, I fix my code. Now it's working

OriginalGriff 22-Feb-23 6:11am

It's still a good idea to move the average calculation into a separate function - it makes code a lot "cleaner" and easier to read.

Auyik 22-Feb-23 8:01am

Thank you very much. I edited my code to include a function that calculates the average. Is it ok the way I did it?

OriginalGriff 22-Feb-23 9:16am

If you did, you didn't show us that code ... :D

Auyik 22-Feb-23 10:39am

Sorry, I edited the original code of the post

OriginalGriff 22-Feb-23 11:17am

I see - no, that isn't what I meant.
Move the whole task into a function - pass it the value of y (in case it needs it later) and the number of random numbers to generate. It generates them, calculates the average, and returns that.

That way, you have a "module" you can test and be damn sure it works, and it will be flexible if the number of samples increases without any change in it's code!

All you have to do than is provide the loop to work your way through y which calls the new function and prints the result each time it goes round.

Your code gets cleaner and easier to understand - instead of the mess it is at the moment because it has "evolved" into its present shape (probably by guesswork :D ).

Auyik 5-Mar-23 20:50pm

Thanks! I got it :)

OriginalGriff 6-Mar-23 0:54am

Excellent!

merano99 · Answer 2 · 2023-02-22T12:39:00

Quote:
Auyik 10hrs 10mins ago
I edited my code to include a function that calculates the average. Is it ok the way I did it?

no!

C++

float mean(float sum, float counts){
   double mean = 0.0;
   mean = sum/counts;
   return mean;
}

It is almost useless to calculate the mean value over a single value and divide it by count.

Here several values should be passed, as well as the number of values as parameter. After that you would need a loop in which you sum up the values and finally it would make sense to divide.

CPallini · Answer 3 · 2023-02-21T20:40:00

Quote:
r = rand()/(float)RAND_MAX;

That should be, instead

C

r = rand()/(RAND_MAX + 1.0f);

Then you forgot to reset the sum_r variable inside the ITERATIONS loop.

Try

C

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

#define L 2
#define STEPS 10
#define ITERATIONS L*L


int main()
{
    FILE * doc = fopen("document.txt","w");
    float y=0.0f;
    srand((unsigned)time(0));

    while(y < 1.0f)
    {
        for(int iter = 0; iter < ITERATIONS ; iter++)
        {
            float sum_r = 0.0f;

            for (int t = 0; t < STEPS; t++)
            {
                float r = rand()/(RAND_MAX+1.0f);
                fprintf(doc,"r=%f\n",r );
                sum_r += r;
            }
            float mean_r = sum_r/STEPS;

           fprintf(doc," %f    %d      %f\n\n",y, iter, mean_r);
        }
        y = y + 0.01f;
    }
    fclose(doc);
    return 0;
}

How to calculate the average of a set of random numbers including additional conditions in C?

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