C++ program to calculate electric bill

#include <iostream>
using namespace std;
int main ()
{
int a,b;
cout<<" DESIGNED BY : MUHAMMAD REHAN ASGHAR" <<endl;
cout<<" ELECTRICITY BILL CALCULATOR" <<endl;

cout<<" ENTER YOUR UNITS \n";
cin>> a;

if (a<=100)

{
b=a*3;
cout<<"  YOUR BILL IS \n";
cout<< b;
}

else if (a<=300)

{
b=(100*3)+(a-100)*7;
cout<<"  YOUR BILL IS \n";
cout<< b;
}

else if (a>300)

{
b=(100*3)+(200*7)+(a-300)*11;
cout<<"  YOUR BILL WILL BE\n";
cout<< b;
}
return 0;
}