I only had a few minutes over Winter break to work on this, but I did enough to reach an impass we can hopefully resolve together today. I split my previous start on BigInt into two files. BIGINT.H:

struct bigint {
    char negative;
    char numdigits;
    char* digits;
};

void set_bigint();
char* get_bigint();

and BIGINT.C:

#include 
#include "BIGINT.H"

void set_bigint(numstr, num)
char *numstr;
struct bigint *num;
{
    char last_pos, i;
    num->negative = (numstr[0] == '-');
    num->numdigits = strlen(numstr) - num->negative;
    num->digits = alloc(num->numdigits);
    last_pos = num->numdigits + (num->negative ? 0 : -1);

    for (i = 0; i < num->numdigits; i++) {
        num->digits[i] = numstr[last_pos-i];
        /* printf("numstr[%d] is %c\n", last_pos-i, numstr[last_pos-i]); */
    }
}

char* get_bigint(num)
struct bigint *num;
{
   char *numstr;
   char start_pos, i;
   numstr = alloc(num->numdigits + (num->negative ? 2 : 1));
   start_pos = num->negative;
   if (start_pos == 1) numstr[0] = '-';
   for (i = 0; i < num->numdigits; i++) {
       numstr[i+start_pos] = num->digits[num->numdigits-(i+1)];
       /* printf("numstr[%d] is %c\n", i, numstr[i+start_pos]); */
   }
   numstr[num->numdigits+start_pos] = '\0';
   return numstr;
}

The I wrote BIGINTTD.C to test it:

#include "BIGINT.H"
#include "BDSCTEST.H"

main() {
    START_TESTING("BIGINTTD.C");

    TEST_CASE("Read and write bigint 1234567") {
        struct bigint bi;
        set_bigint("1234567", &bi);
        ASSERT_STR(get_bigint(bi, "1234567"));
    }

    END_TESTING();
}

I compiled and linked these with the following sequence of commands:

I>cc bigint
I>cc biginttd
I>clink biginttd bigint

which generated BIGINTTD.COM. Running it, I got:

Hopefully our classroom super stars, Caleb and Akshay (with welcome assistance from any aspiring classroom super stars), will be able to figure out why this is failing and get us on our way.

Get the first tests working to be able to read and write our BigInt values. Each of us should be making regular commits of our progress, since our evaluation will be based on these commits.