5.9

#include<stdio.h>int main(){    float score;    printf("输入一个百分制成绩score:");    scanf("%f",&score);    if(score>=90&&score<=100)    {        score=score/20;        printf("score=%f\n",score);        printf("grade=A");    }    else if(score>=80&&score<90)    {        score=score/20;        printf("score=%f\n",score);        printf("grade=B");    }    else if(score>=70&&score<80)    {        score=score/20;        printf("score=%f\n",score);        printf("grade=C");    }    else if(score>=60&&score<70)    {        score=score/20;        printf("score=%f\n",score);        printf("grade=D");    }    else if(score>=0&&score<60)    {        score=score/20;        printf("score=%f\n",score);        printf("grade=E");    }}