Complementing a Strand of DNA

Problem
In DNA strings, symbols 'A' and 'T' are complements of each other, as are 'C' and 'G'.
The reverse complement of a DNA string s is the string sc formed by reversing the symbols of s, then taking the complement of each symbol (e.g., the reverse complement of "GTCA" is "TGAC").
Given: A DNA string s of length at most 1000 bp.
Return: The reverse complement sc of s.
Sample Dataset
AAAACCCGGT
Sample Output

ACCGGGTTTT

#include <stdio.h>
void main ()
{
	char s[9999];
	int i=0;
	int cnt  =0;
	int cnt_a=0;
	int cnt_c=0;
	int cnt_g=0;
	int cnt_t=0;
	puts("输入:\n");
	gets(s);
	for(i=0;s[i]!='\0';i++)
	{
	
		if (s[i] == 'C')
		{
			s[i]  = 'G';
			continue;
		}

		if (s[i] == 'G')
		{
			s[i]  = 'C';
			continue;
		}

		if (s[i] == 'T')
		{
			s[i]  = 'A';
			continue;
		}

		if (s[i] == 'A')
		{
			s[i]  = 'T';
			continue;			
		}

	}
	cnt = i;
	for(;cnt>0;cnt--)
	{
		printf("%c",s[cnt-1]);
	}
}