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

int to-upper(char *s);

int isupper;

int main()
{
    char tmp[10];
    isupper = 0;

    srand(time(NULL));

    some loop {
        isupper = decide on upper or lower;
        sprintf(tmp, "%s" to-upper((rand() % 4) > 0 : "on" "n"));
        printf("%s" tmp);
        etc;
        printf("\n");
    }
    return 0;
}
int to-upper(char *s)
{
    int i;

    if (isupper) {
        for (i = 0; s[i]; i++)
            s[i] = toupper(s[i]);
    }
    return s;
}