阶梯电价
#include<iostream>
#include<iomanip>
using namespace std;
int main()
{
float a,cost;
cin>>a;
if(a<0) {cout<<“Invalid Value!”;} else if(a<=50) {cost=0.53a;
cout<<setiosflags(ios::fixed
<<setprecision(2);
cout<<"cost = "<<cost;}
else {cost=0.58(a-50)+26.5; cout<<setiosflags(ios::fixed)<<setprecision(2);
cout<<"cost = "<<cost<<endl;} return 0;}