C problem

Example: Input DNA sequence: ATGACACGGAGTACGTAA The locations of the triples encoding Threonine are: 3 (ACA) and 12 (ACG). Notice that the location 5 is not an answer, since every triple has to start on a multiple of three index (otherwise triples would overlap). Error handling and output: If the program is given an invalid strand (i.e., one that contains characters other that A, T, C, and G), it should print -1 and terminate. If the program is given a valid strand that does not contain even one triple, the program should print -2 and terminate. If the program is given a valid strand that contains one or more triples, it should print the indexes of the first character of the triple, one per line. In the above example, the output should be: 12 Note: You should assume that the input sequence is all in uppercase. You can treat any lowercase letters as invalid characters. The maximum length of the sequence that your program needs to handle is 9,999