请教一下这个用c语言怎么做

#include<stdio.h>

void statistic(char *s,int *letter,int *space ,int *digit,int *other)
{
    if(s == NULL) return ;
    for(int i=0;i<strlen(s);++i)
    {
        if(isalpha(s[i])) ++(*letter);
        else if(isdigit(s[i])) ++(*digit);
        else if(isspace(s[i])) ++(*space);
        else ++(*other);
    }
}


int main()
{
    printf("string=");
    char str[100];
    gets(str);
    printf("total:%d\n",strlen(str));
    int letter=0, space=0 ,digit=0,other=0;
    statistic(str,&letter,&space ,&digit,&other);
    printf("letter:%d,digit:%d,space:%d,others:%d\n",letter,digit,space,other);


    return 0;
}