求解答，请问怎么改，是不可以连用吗？

#include
int main()
{
char grade,score;
int range;
printf("input grade:\n");
scanf("%c",&grade);
if(grade='A')
printf("score>=90\n");

if(grade='B')
    printf("80<=score<90\n");

if(grade='C')
    printf("70<=score<80\n");

if(grade='D')
    printf("60<=score<70\n");

if(grade='E')
    printf("score<=60\n");

return 0;

}

if(grade=='B')
判断相等用==，而=是赋值