程序代码：

#include<iostream>
#include<string>
#include<cctype>
using namespace::std;
    int main(){
        string st;
    cout<<"Enter some string"<<endl;
    cin>>st;
    int a,b,c,d;
    for(string::size_type ix=0;ix!=st.size();++ix){
        if(isalpha(st[ix])){
        ++a;}
        if(isdigit(st[ix])){
        ++b;    }
        if(isspace(st[ix])){
            ++c;    }
        if(ispunct(st[ix])){
            ++d;    }
    }

cout<<a<<endl;
cout<<b<<endl;
cout<<c<<endl;
cout<<d<<endl;
return 0;
}