If you want to know more: http://en.wikipedia.org/wiki/DNA

In DNA strings, symbols “A” and “T” are complements of each other, as “C” and “G”. Your function receives one side of the DNA (string, except for Haskell); you need to return the other complementary side. DNA strand is never empty or there is no DNA at all (again, except for Haskell).

More similar exercise are found here: http://rosalind.info/problems/list-view/ (source)

Example: (input –> output)

"ATTGC" --> "TAACG"
"GTAT" --> "CATA"

The problem link is here.

Solution:

#include <string.h>

char *dna_strand(const char *dna)
{

  int len = strlen(dna);
  int i;
  char *cdna = calloc(len + 1, sizeof(char));
  char temp;

  strcpy(cdna, "");

  for (i = 0; i < len; i++)
  {
    if (dna[i] == 'A')
    {
      temp = 'T';
      strncat(cdna, &temp, 1);
    }
    else if (dna[i] == 'T')
    {
      temp = 'A';
      strncat(cdna, &temp, 1);
    }
    else if (dna[i] == 'C')
    {
      temp = 'G';
      strncat(cdna, &temp, 1);
    }
    else if (dna[i] == 'G')
    {
      temp = 'C';
      strncat(cdna, &temp, 1);
    }
  }
  return cdna;
}

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