程序如下：
# include <stdio.h>
void main()
{
    int num,alp_a,alp_A,oth;
    char a;
    num=0;
    alp_a=0;
    alp_A=0;
    oth=0;
    printf("本程序负责统计输入的字符的类型\n");
    printf("类型有大写字母、小写字母、数字、其他字符\n");
    printf("请输入字符，以ESC退出\n");
    while((a=getchar()))
    {
        switch (a)
        {
            case a>='a' && a<='z':
                alp_a ++;
                break;

            case a>='A' && a<='Z':
                alp_A ++;
                break;
            case a>='0' && a<='9':
                num ++;
                break;
            default:
                oth ++;
                break;
        }
        printf("请输入下一个字符：\n");
    }
    printf("统计结果如下：\n");
    printf("小写字母的个数为：%d",alp_a);
    printf("大写字母的个数为：%d",alp_A);
    printf("数字的个数为：%d",num);
    printf("其他的个数为：%d",oth);
}
编译环境：code：：blocks
提示错误：
\num_aip\num_alp.c|2|warning: return type of 'main' is not 'int'|
\num_aip\num_alp.c||In function 'main':|
\num_aip\num_alp.c|17|error: case label does not reduce to an integer constant|
\num_aip\num_alp.c|20|error: case label does not reduce to an integer constant|
\num_aip\num_alp.c|23|error: case label does not reduce to an integer constant|
||=== Build finished: 3 errors, 1 warnings ===|

明白了，非常感谢