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]);}}