C语言；显示输入消息的长度

#include<stdio.h>
int main()
{
char ch;

int len = 0;
ch = getchar();
while (ch != '\n')
{
    len++;
    ch = getchar();
}
printf("Your massage was %d character(s) long.\n",len);
return 0;

}
请问这个代码while里面为什么还要加一行ch = getchar();

输出ch