输出字符串的长度……求大神找错

#include<stdio.h>
void main()
{
int len,i=0;
char ch;
printf("please input a string:\n");
ch=getchar();
while (ch!='\n');
{
i++;
ch=getchar();
}
len=i;
printf("the string has %d characters.",len);
}
getchar神马的完全不会啊→_→I