方法1
#include <stdio.h>
main()
{
    char   ch ;
    printf("从键盘输入一个字符\n");
    scanf("%d",&ch);
    ch=getchar();
    if(97<=ch && ch<=122)
    {
        printf("该字符为小写字母");
        putchar('\n');
    }
    else if(65<=ch && ch<=90)
    {
         printf("该字符为大写字母");
        putchar('\n');
    }
    else if(48 <=ch && ch<=57)
    {
         printf("该字符为数字");
         putchar('\n');
    }
    else if(ch == 32)
    {
         printf("该字符为空格");;
        putchar('\n');
    }
    else
    {
         printf("该字符为其它");
        putchar('\n');
    }
方法二

#include<stdio.h>
int main(   )
{
         char ch;
         printf("Please enter a char:\n");
         ch=getchar();
         if(ch>='0'&&ch<='9')
           {
               printf("%c是数字字符",ch);
            }
         else if(ch>='a'&&ch<='z')
         {
               printf("%c是小写字母",ch);
         }
         else if(ch>='A'&&ch<='Z')
         {
               printf("%c是大写字母",ch);
         }
         else if(ch==' ')
         {
               printf("%c是空格",ch);
         }
         else
         {
               printf("%c是其它字符",ch);
         }
         return 0;
}

用scanf和getchar随便那一种都行吧。

第一种是把输入字符转化成ASCII代码进行判断，而第二种是直接进行判断，所以不需要输入

谢谢

谢谢