Random Number Generation of Combination of six numbers

I am doing a Pseudo Random Number Generator that creates 100 combinations with no repetition of 5 numbers from 1 to 56 and then it saves them on a text file. Like this:

33 28 46 7 30 57 
15 29 43 41 16 21 
11 43 7 18 31 25 
36 32 19 42 47 33 
46 13 14 1 28 25 
33 14 55 43 29 13 
30 14 12 45 46 32 
56 31 54 32 20 21 
10 52 40 57 31 14 
28 44 15 47 57 45 
...

This is my code, but I feel that it is a little bit too big, specially the part when is checking no repetitions of the numbers

// Including C Standard Libraries
#include <stdint.h>  
#include<stdio.h> 
#include<stdlib.h> 
#include<time.h> 

int main() 
{ 
    // Initialing Random Generation C Library
    srand(time(NULL)); 

    // Variables for PRNG Loop
    uint16_t i;  
    uint8_t j; 

    uint8_t x[6] = {0,0,0,0,0,0};

    // Opening File to save Results
    FILE *fp;
    fp = fopen("combinations.txt", "w+"); 

    // PRNF Loop
    for(i = 0; i<100; i++)  // Numbers of Combinations 
    {
        for(j = 0; j<6; j++)  // Number of Elements of the Combinations
        {
            x[j] = rand() % 57 + 1;  // Generating Random Number

            // Avoiding Repetition of Numbers
            if ( j==1)
            {
                while(x[1] == x[0])
                {
                    x[1] = rand() % 57 + 1;
                }
            }
            if ( j==2)
            {
                while(x[2] == x[0] || x[2] == x[1])
                {
                    x[2] = rand() % 57 + 1;
                }
            }
            if ( j==3)
            {
                while(x[3] == x[0] || x[3] == x[1] || x[3] == x[2] )
                {
                    x[3] = rand() % 57 + 1;
                }
            }
            if ( j==4)
            {
                while(x[4] == x[0] || x[4] == x[1] || x[4] == x[2] || x[4] == x[3] )
                {
                    x[4] = rand() % 57 + 1;
                }
            }
            if ( j==5)
            {
                while(x[5] == x[0] || x[5] == x[1] || x[5] == x[2] || x[5] == x[3] || x[5] == x[4] )
                {
                    x[5] = rand() % 57 + 1;
                }
            }


            fprintf(fp, "%d", x[j]);  // Saving Random Number in File
            fprintf(fp, " "); 
        } 

        fprintf(fp, "\n");  // Saving Newline  

        for (int i = 0; i < 6; ++i)
        {
            x[i] = 0;
        }    

    }

    fclose(fp);
} 

Is there a way to improve the code?