Generating alphanumeric gibberish?

What's a simple (preferably loopless) way to generate a large amount of alphanumeric gibberish? Any language is acceptable.

In PHP, I thought this would be perfect:

hexdec(mt_rand(1.e999999999, 1.e9999999999));

But it doesn't work due to restrictions on the length of int. :(

ENTERPRISE C IMPLEMENTATION

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

char characters[] = "1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghjklmopqrst";
char gibberish[1];

int main()
{
    srand(time(NULL));
    int x;
   
    for (x = 0; x <= 300; x++) gibberish[x] = characters[rand() % 54];
    for (x = 0; x <= 300; x++) printf("%c", gibberish[x]);
   
    return 0;
}