test_of_c_function_rand()_v1.c

/*

    test_of_c_function_rand()_v1.c


    You can find all my C programs at Dragan Milicev's pastebin:

    https://pastebin.com/u/dmilicev

*/

#include <stdio.h>
#include <stdlib.h>         // for RAND_MAX = 32767
#include <time.h>           // for random numbers, for function rand()


int main()
{                           // try n = 10, 100, 1000, RAND_MAX
                            // try repeat_times = 1, 10, 100, 1000, RAND_MAX = 32767
    int i, j, n=100, repeat_times=RAND_MAX;
    int random_number, pass_of_loop=0, min_appearance, max_appearance;
    int counter_array[RAND_MAX];            // array to count frequency of random numbers
    time_t t;                               // for random number generator


    // Intializes random number generator, should only be called once.
    //srand((unsigned) time(0));
    srand((unsigned) time(&t));

    // reset all n counters in counter_array[] to 0
    for( i=0; i<n; i++ )
        counter_array[i] = 0;

    // counting the pass_of_loop of random numbers
    for( j=0; j<repeat_times; j++ )
    {
        for( i=0; i<n; i++ )
        {
            random_number = rand() % n;     // random number between 0 and n-1
            counter_array[random_number]++; // increase the corresponding counter
        }

        // count and display loop passes
        printf("\n %8d. pass of loop ", ++pass_of_loop);
    }


    // finding the lowest and highest pass_of_loop
    min_appearance = counter_array[0];          // we assume it is the smallest
    max_appearance = 0;                         // we assume it is the largest

    for( i=0; i<n; i++ )
    {
        if( min_appearance > counter_array[i] )
            min_appearance = counter_array[i];

        if( max_appearance < counter_array[i] )
            max_appearance = counter_array[i];
    }


    // print the number of occurrences of random numbers
    for( i=0; i<n; i++ )
        printf("\n %7d %7d ", i, counter_array[i] );

    // print the lowest and highest frequency
    printf("\n\n highest frequency is %7d \n", max_appearance );
    printf("\n lowest frequency is  %7d \n", min_appearance );
    printf("\n %7d    - %7d = %5d \n",
            max_appearance, min_appearance, max_appearance - min_appearance );


    return 0;
}