#include <stdio.h>
#include <stdlib.h>
 
int convertBase(unsigned long n, unsigned base,
                   char *dst, size_t dlen)
{
    static const char alpha[] = "0123456789abcdef";
    char *p = dst, *q = dst;
 
    // invalid base filter
    if (base == 1 || base >= sizeof(alpha) || dlen < 1)
        return -1;
 
    // conversion
    while (p-dst < dlen-1)
    {
        *p++ = alpha[ n % base ];
        if ((n /= base) == 0)
            break;
    }
 
    // ran out of space?
    if (n)
        return -1;
 
    // terminate and reverse
    *p = 0;
    while (q < p--)
    {
        char c = *q;
        *q++ = *p;
        *p = c;
    }
    return 0;
}
 
int main(void)
{
    unsigned long int n = 1000000000U;
    char buff[65];
 
    for (unsigned int i=2; i<=16; ++i)
    {
        printf("%lu in Base %u = ", n, i);
        if (convertBase(n, i, buff, sizeof(buff)) == 0)
            puts(buff);
    }
 
    return 0;
}

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