C语言switch语句case匹配counter输出年龄阶段问题求助

核心错误点梳理 #

• 成年/未成年判断逻辑错误：你将Age < 18的判断嵌套在了Age > 18的分支内部，该分支永远不可能触发，未成年提示永远不会输出。
• 分段计数器counter计算逻辑完全失效：现有代码中while (++counter <= 10);末尾跟了空语句分号，只要年龄小于等于100，计数器就会从0一直自增到11才停止，和年龄完全没有关联，自然无法匹配switch的对应case。
• 缺少年龄合法性校验：如果用户输入的出生年份大于当前年份，会得到负数年龄，没有对应的处理逻辑。

修复思路 #

你的switch分支编号刚好对应年龄十位上的数值，完全不需要循环计算，直接用C语言整数除法的特性（截断小数）就能得到正确的counter值：

• 0-9岁除以10得到0，对应case 0
• 10-19岁除以10得到1，对应case 1，刚好输出你需要的you are in your tens / teens
• 20-29岁除以10得到2，对应case 2，以此类推
• 超过100岁直接赋值counter为10即可

修复后的完整代码 #

#include <stdio.h>

int main()
{
    int YoB, CY, Age;
    unsigned int counter = 0;
    printf("Please enter your year of birth: ");
    // 若使用非VS编译器，请将scanf_s改为scanf
    scanf_s("%d", &YoB);
    printf("Please enter the current year: ");
    scanf_s("%d", &CY);
    Age = CY - YoB;
    printf("Entered year of birth %d\n", YoB);
    printf("Entered current year %d\n", CY);
    printf("You are %d years old\n \n", Age);

    // 修复成年/未成年判断逻辑
    if (Age >= 18) {
        puts("You are an adult\n");
    } else {
        puts("You are a minor\n");
    }

    // 年龄合法性校验
    if (Age < 0) {
        puts("invalid age!");
        return 0;
    }

    // 修复counter计算逻辑
    if (Age > 100) {
        counter = 10;
    } else {
        counter = Age / 10;
    }

    switch (counter) {
    case 0:
        puts("You are less than 10\n");
        break;
    case 1:
        puts("you are in your tens / teens\n");
        break;
    case 2:
        puts("You are in your twenties\n");
        break;
    case 3:
        puts("You are in your thirties\n");
        break;
    case 4:
        puts("You are in your fourties\n");
        break;
    case 5:
        puts("You are in your fifties\n");
        break;
    case 6:
        puts("You are in your sixties\n");
        break;
    case 7:
        puts("You are in your seventies\n");
        break;
    case 8:
        puts("You are in your eighties\n");
        break;
    case 9:
        puts("You are in your nineties\n");
        break;
    case 10:
        puts("You are a 100+!!\n");
        break;
    default:
        puts("invalid age!");
        break;
    }
    return 0;
}

内容的提问来源于stack exchange，提问作者fvaisal