Get bases for decimal nubmers

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

#define SIZE sizeof(unsigned)* CHAR_BIT
//#define DEBUG

int main(void){


    char digits[]={'0', '1', '2', '3', '4', '5', '6', '7', '8', 
                 '9', 'A', 'B', 'C', 'D', 'E', 'F'};
    char ret[SIZE] = {0};
    unsigned n, b;

    printf("Enter a Positive number? " );
    scanf("%u", &n);
    printf("Enter Base? " );
    scanf("%u", &b);
    
    int i=0;
    do{
        ret[i++] = n%b;
        n /=b;

    }while (n>0);

#ifdef DEBUG
    for (i=0; i<SIZE;i++)
        printf("%i", ret[i]);
    printf("\n");
#endif

    // SWAP:
    for (i=0; i<SIZE/2;i++){
        int tmp=ret[i];
        ret[i] = ret[SIZE-i-1];
        ret[SIZE-i-1] = tmp;
    }

    for (i=0; i<SIZE;i++)
        printf("%c", digits[ret[i]]);

    
    printf("\n");
    return 0;
}