gistfile1.c

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

char* cycle(int start, int next, int repeatafter, int windowsize){
    int j;
    char *str = malloc( sizeof(char) * windowsize + 1);

    for(j=0;j < windowsize; ++j)
        str[j] = 0x30 + ((start + next*j) % (repeatafter+1)); 
    str[j] = '\0';

    return str;
}

int main(int argc, const char *argv[])
{
    int i;
    for(i=0; i < 10; ++i)
        printf("%s\n" , cycle(i, 1, 5, 3));

    return 0;
}