random_numbers_without_repeating.c

/*
    random_numbers_without_repeating.c

Fills in the array with random numbers without repeating numbers.

Necessary code lines to generate random numbers:

#include<stdlib.h>  // RAND_MAX is defined in stdlib.h
#include<time.h>    // for random number generator

in function main() :

    int number;
    time_t t;   // for random number generator

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

    // function rand() returns an integer value between 0 and RAND_MAX.
    number = rand();
    // or
    number = rand() % 9 + 1;    // generate random number between 1 and 9

*/

#include<stdio.h>
#include<stdlib.h>  // RAND_MAX is defined in stdlib.h
#include<time.h>    // for random number generator

#define ARRAY_SIZE  100


// generate and return random integer number between lower and upper, including them.
int get_random_integer_from_lower_to_uppper(int lower, int upper)
{
    // generate and return random number between 0 and upper-1
    //return( rand() % upper );

    // generate and return random number between 1 and upper
    //return( rand() % upper + 1 );

    // generate and return random integer number between lower and upper
    return( (rand() % (upper - lower + 1)) + lower );
} // get_random_integer_from_lower_to_uppper()


// Returns unique random integer between lower and upper,
// different from numbers in array[] of n integers
int get_unique_number( int array[], int n, int lower, int upper )
{
    int i, number, unique;

    if( (upper-lower)< n ) {
        printf("\n Can't find %d unique elements from %d numbers ! \n", n+1, upper-lower+1);
        exit(1);
    }

    if( lower >= upper ) {
        printf("\n Lower is greater than or equal than upper ! \n", n+1, upper-lower+1);
        exit(1);
    }

    while( 1 ) {
        i=0;                        // reset i
        unique = 1;                 // reset flag unique
        number = get_random_integer_from_lower_to_uppper(lower, upper);

        while( i<n && unique ) {    // for all array elements, while unique!=0
            if( array[i] == number ) {
                unique = 0;         // than number isn't unique in the array[]
            }
            i++;                    // move on to the next element of array[]
        } // while( i<n && unique )

        if( unique )                // if number is unique in array[]
            return number;
        else                        // if it isn't unique, get another random integer
            number = get_random_integer_from_lower_to_uppper(lower,upper);
    } // while(1)
} // get_unique_number()



int main(void)
{
    int i, n=ARRAY_SIZE, min=1, max=32000;
    int array[ARRAY_SIZE];              // array for unique integers
    time_t t;                           // for random number generator

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

    for(i=0; i<n; i++) {
        array[i] = get_unique_number( array, i, min, max );
    }

    printf("\n Array of %d random integers between %d and %d is: \n", n, min, max);

    for(i=0; i<n; i++) {                // print array on screen, 13 in one line

        if( i%13==0)
            printf("\n");

        printf("%6d", array[i]);
    }

    printf("\n");

    return(0);
} // main()