分类统计字符个数：输入一行字符，统计出其中的英文字母、空格、

#define _CRT_SECURE_NO_WARNINGS    
//#include <stdlib.h> 
#include <stdio.h>
//#include<malloc.h>
//#include<math.h>
//#include <string.h>
#include <ctype.h> //字符处理 

int main() {
    char input_string[100];
    int letter_count = 0, space_count = 0, digit_count = 0, other_count = 0;

    printf("请输入一行字符：");
    fgets(input_string, 100, stdin);

    for (int i = 0; input_string[i] != '\0'; i++) {
        if (isalpha(input_string[i])) {
            letter_count++;
        }
        else if (isspace(input_string[i])) {
            space_count++;
        }
        else if (isdigit(input_string[i])) {
            digit_count++;
        }
        else {
            other_count++;
        }
    }

    printf("英文字母个数：%d\n", letter_count);
    printf("空格个数：%d\n", space_count);
    printf("数字个数：%d\n", digit_count);
    printf("其他字符个数：%d\n", other_count);

    return 0;
}


    

为什么这样子写不行呢？

#include<stdio.h>
int main(void)
{
	int in,blank,digit,other;
	char ch;
	scanf("%c",&ch);
	while(ch!='\n'){
		switch(ch){
			case(ch>'a' && ch<'z'):
				in++;
				break;
			case(ch>'A'&&ch<'Z'):
				in++;
				break;
			case' ':
				blank++;
				break;
			case'0':case'1':case'2':case'3':case'4':case'5':case'6':case'7':case'8':case'9':
				digit++;
				break;
			default:
				other++;
				break;
		}
		scanf("%c",&ch);
	}
	printf("英文字符为%d个，空格为%d个，数字为%d个，其他字符为%d个",in,blank,digit,other);
	return 0;
}

# include <stdio.h>
# include <iostream>
# include <string.h>

using namespace std;

int main()
{
    char ch;
    
    int a,b,c,d;
 
    a=b=c=d=0;
    ch=getchar();
    while(ch != '\n')
    {
       if((ch>='a'&&ch<='z')||(ch>='A'&&ch<='Z'))
           a++;
       else if(ch == ' ')
           b++;
       else if(ch>=0&&ch<=0)
           c++;
       else
           d++;

       ch=getchar();
    }
    printf("letter=%d,blank=%d,digit=%d,other=%d\n",a,b,c,d);
}