一下把原因说出来，不给楼主思考的过程，你这是不是帮楼主呀，马上就要引导楼主到最后一步了，你全说了，没意思了

#include "stdio.h"
void main()
{
    char ch;
    int alph = 0,digit = 0, empty = 0,other =0;
    printf("输入一行字符");
    while((ch = getchar())!= '\n')
    {
        if(ch >= 'a' && ch <= 'z' || ch >= 'A' && ch <= 'Z')
            alph++;
        else if(ch >= '0' && ch <= '9')
            digit++;
        else if(ch == ' ')
            empty++;
        else other++;
    }
    printf("字母的个数为%d\n",alph);
    printf("数字的个数为%d\n",digit);
    printf("空格数为%d\n",empty);
    printf("其它字符的个数为%d\n",other);
}
你自己看下我的和你有什么不一样啊，就是你一个地方没有用好，下面这个也有同样的效果啊，
#include "stdio.h"
void main()
{
    char ch;
    int alph = 0,digit = 0, empty = 0,other =0;
    printf("输入一行字符");
    ch = getchar();
    while(ch!= '\n')
    {
        if(ch >= 'a' && ch <= 'z' || ch >= 'A' && ch <= 'Z')
            alph++;
        else if(ch >= '0' && ch <= '9')
            digit++;
        else if(ch == ' ')
            empty++;
        else other++;
        ch = getchar();
    }
    printf("字母的个数为%d\n",alph);
    printf("数字的个数为%d\n",digit);
    printf("空格数为%d\n",empty);
    printf("其它字符的个数为%d\n",other);
让我们一起努力好好的学习吧

#include "stdio.h"
void main()
{
    char ch;
    int alph=0,digit=0,empty=0,other=0;
    printf("输入一行字符:");
    ch = getchar();
    while(ch!='\n')
    {
    if(ch>='a'&&ch<='z'||ch>='A'&&ch<='Z')
      alph++;
     else if(ch>='0'&&ch<='9')
      digit++;
      else if (ch==' ')
      empty++;
      else other++;
      ch = getchar();
    }
      printf("字母的个数为%d\n",alph);
      printf("数字的个数为%d\n",digit);
       printf("空格数为%d\n",empty);
        printf("其他字符的个数为%d\n",other);
}

是“ch!='\n'”时执行下面，以\n为结束标志
#include <stdio.h>
int main()
{
    char ch;
    int a=0,b=0,c=0,d=0,e=0;
        
    printf("请输入一行字符:\n");
    while((ch=getchar())!='\n')
    {
        if(ch<='z'&&ch>='a')
        {
            a++;
        }
        else if(ch<='Z'&&ch>='A')
        {
            b++;
        }
        else if(ch==' ')
        {
            c++;
        }
        else if(ch<59&&ch>47)
        {
            d++;
        }
        else
        {
            e++;
        }
    }
    printf("小写英文字母：%d\n",a);
    printf("大写英文字母：%d\n",b);
    printf("空格：%d\n",c);
    printf("数字：%d\n",d);
    printf("其他:%d\n",e);
    }
    return 0;
   
}

getchar函数包含在哪个头文件