Transcribing DNA into RNA

Problem
An RNA string is a string formed from the alphabet containing 'A', 'C', 'G', and 'U'.
Given a DNA string t corresponding to a coding strand, its transcribed RNA string u is formed by replacing all occurrences of 'T' in t with 'U' in u.
Given: A DNA string t having length at most 1000 nt.
Return: The transcribed RNA string of t.
Sample Dataset
GATGGAACTTGACTACGTAAATT
Sample Output

GAUGGAACUUGACUACGUAAAUU

#include <stdio.h>
void main ()
{
	char s[9999];
	int i=0;
	int cnt_a=0;
	int cnt_c=0;
	int cnt_g=0;
	int cnt_t=0;
	puts("輸入:\n");
	gets(s);
	for(i=0;s[i]!='\0';i++)
	{
		if (s[i] == 'T')
		{
			s[i]  = 'U';		
		}

	}
	printf("%s",s);
}