输入3个字符串，将它们按照字母由大到小排序

.用string方法定义字符串变量

实现代码：

#include<iostream>
#include<string>
using namespace std;
int main(){
	string a,b,c,t;
	cout<<"please input first string:"<<endl;
	cin>>a;
	cout<<"please input second string:"<<endl;
	cin>>b;
	cout<<"please input third string:"<<endl;
	cin>>c;
	if(a>b){
		t=a;
		a=b;
		b=t;
	}
	if(a>c){
		t=a;
		a=c;
		c=t;
	}
	if(b>c){
		t=b;
		b=c;
		c=t;
	}
	cout<<a<<"<<"<<b<<"<<"<<c<<endl;    
	return 0;	
}