Replacing all duplicate numbers in an Array, so that every element is unique in C

The elements in the array are created using rand().

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

int main(void){
    int array[6] = { 0 };
    
    srand(time(NULL));
    
    for(int i = 0; i < 6; i++){
        array[i] = rand() % 49 + 1;
    }
    
    /*
        Code to check for duplicates
        if duplicate found
            duplicate = rand(49);
    */
    
    for(int i = 0; i<6; i++){
            printf("[%d]",array[i]);
        }
    
    return 0;
}

I don´t really want to sort the array if it makes it easier to find duplicates because the array is for a lottery ticket. I have tried different methods, but all of them are inefficient and includes a lot of loops. I had different approaches, but all of them didn´t really work, because what if, the newly created number, is yet again a duplicate? Or if the last number in the array is a duplicate. So I came with the following approach: The algorithm will create as many areas, as long no number in the array is a duplicate

#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#define TRUE 1

int main(void) {
    int a[6] = {0};
    srand(time(NULL));

    while (TRUE) {

        int c = 0;

        for (int i = 0; i < 6; i++) {
            a[i] = rand() % 49 + 1;
        }

        for (int i = 0; i < 6; i++) {
            for (int j = i + 1; j < 6; j++) {
                if (a[i] == a[j]) {
                    c++;
                }
            }
        }
        if (c == 0) {
            break;
        }
    }
    
    for (int i = 0; i < 6; i++) {
        printf("%d\n", a[i]);
    }

    return 0;
}

Any Ideas, how to make an easy, efficient, but not so complex algorithm for a beginner?

Thanks :)