请问为什么错误提示要左操作数

Question

#include
#define i 0
int main(void)
{
char letter;
while(letter=getchar()!='#')
{
printf("%c %d",letter,letter);
i++;
if(i==8)
break;
}
printf("\n");
return 0;
}

Answer 1

while(letter=getchar()!='#')
->
while((letter=getchar())!='#')