#include <stdio.h>
 
int main() {
    int score;
 
    // 输入提示
    printf("请输入考试成绩（0-100）: ");
 
    // 读取用户输入
    if(scanf("%d", &score) != 1) {
        printf("输入错误，请输入数字！\n");
        return 1;
    }
 
    // 分支判断结构
    if(score < 0 || score > 100) {
        printf("成绩无效，请输入0-100之间的数值\n");
    } 
    else if(score >= 90) {
        printf("成绩等级: A\n");
    } 
    else if(score >= 80) {
        printf("成绩等级: B\n");
    } 
    else if(score >= 70) {
        printf("成绩等级: C\n");
    } 
    else if(score >= 60) {
        printf("成绩等级: D\n");
    } 
    else {
        printf("成绩等级: E（不及格）\n");
    }
 
    return 0;
}

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