// In DNA strings, symbols "A" and "T" are complements of each other, as "C" and "G". You have function with one side of the DNA (string, except for Haskell); you need to get the other complementary side. DNA strand is never empty or there is no DNA at all (again, except for Haskell).

// Example: (input: output)

// dna_strand("ATTGC") /* return "TAACG" */
// dna_strand("GTAT")  /* return "CATA"  */

#include <stdlib.h>
#include <string.h>

char *dna_strand(const char *dna)
{
    char     *out;
    unsigned  idx;

    out = calloc(1, strlen(dna) + 1);
    for(idx = 0; dna[idx]; ++idx)
        out[idx] = (2652 / (11 * dna[idx] - 703) + 703) / 11;

    return out;
}