C++问题~1

//1. Write a program that reads from the keyboard a line of text and
　　//then computes and displays the number of upper case letter, lower
　　//case letters and digits in the line. Make and use your own functions
　　//isupper, islower, and isdigsit.

　　#include<iostream>
　　#include<string>
　　using namespace std;

　　bool isupper(char c)
　　{
　　if('A'<=c&&c<='Z')
　　return true;
　　return false;
　　}

　　bool islower(char c)
　　{
　　if('a'<=c&&c<='z')
　　return true;
　　return false;
　　}

　　bool isdigsit(char c)
　　{
　　if('0'<=c&&c<='9')
　　return true;
　　return false;
　　}

　　void main()
　　{
　　string str;
　　cout<<"Enter the text:";
　　cin>>str;
　　cout<<endl;

　　int num=0;
　　int low=0;
　　int upp=0;