Can anyone Simplify this program related to calculating train fare? - c++

Question

Take the input of kilometers, and the class of journey(1, 2 or 3 for first, second and third class respectively), for a train journey. The program should then calculate the fare of the journey based on the following criteria:
I Could not do the program in one single equation, so I did it using if else statements. Can this program be made shorter and can the logic be designed without the need of the if else statements? Can the logic of the program be represented as a single mathematical equation(using only arithmetic operators)?
My Code:
//
// main.cpp
// c++
//
// Created by Aniansh Raj on 14/08/16.
// Copyright © 2016 Aniansh Raj. All rights reserved.
//
#include <iostream>
using namespace std;
int main()
{
unsigned int km, cl, amt;float r1, r2, r3;
cout<<"Enter distance in kilometer\n";
cin>>km;
cout<<"Enter Class(1, 2 or 3)\n";
cin>>cl;
switch(cl)
{
case 1:
r1=3;r2=2.5;r3=2;break;
case 2:
r1=2;r2=1.5;r3=1;break;
case 3:
r1=1.5;r2=1;r3=0.5;break;
default:
cout<<"Error!\n";
return 0;
}
if(km>=100&&km<=250)
amt=(100*r1)+(km-100)*r2;
else if(km>250)
amt=(100*r1)+(150*r2)+(amt-250)*r3;
else
amt=km*r1;
cout<<endl<<amt;
}

Answer 1

You can reorganize your code in many ways, but I don't think you could obtain exactly what you want.
For example you can store the prices in an array:
unsigned int price[3][3] = {
{300, 250, 200}, // first class, Rupee cents per km
{200, 150, 100}, // second class
{150, 100, 50}, // third class
};
Ask for the distance and the class, then calculate and print the amuont like this:
unsigned int amount;
if ( d <= 100 )
amount = d * price[c][0]; // c = cl - 1; considering your code
else if ( d <= 250 )
amount = 100 * price[c][0] + (d - 100) * price[c][1];
else
amount = 100 * price[c][0] + 150 * price[c][1] + (d - 250) * price[c][2];
std::cout << "distance: " << d << " price: " << amount / 100.0 << '\n';
Now, we can simplify those (linear) equations noticing that are of the form:
amount = constant + d * price
And precalculate the first part, which happens to be the same for all classes and depends only on the range. So, given this array:
unsigned int p0[] = {0, 5000, 17500};
The previous snippet can be rewritten (and "simplified") like this:
unsigned int index = d < 250 ? ( d < 100 ? 0 : 1 ) : 2;
unsigned int amount = p0[index] + d * price[cl - 1][index];
std::cout << "distance: " << d << " price: " << amount / 100.0 << '\n';
One other option, which only hides the conditional part inside a library function, can be:
unsigned int amount = std::min({
p0[0] + d * price[cl - 1][0],
p0[1] + d * price[cl - 1][1],
p0[2] + d * price[cl - 1][2]
});
std::cout << "distance: " << d << " price: " << amount / 100.0 << '\n';

Answer 2

Strictly speaking there's an equivalent ternary statement of
if(km>=100&&km<=250)
amt=(100*r1)+(km-100)*r2;
else if(km>250)
amt=(100*r1)+(150*r2)+(amt-250)*r3;
else
amt=km*r1;
in the form of
amt = (km>=100&&km<=250) ? (100*r1)+(km-100)*r2 : (km>250) ? (100*r1)+(150*r2)+(amt-250)*r3 : km*r1;
Which isn't really as readable as the prior block. If what you're looking for is to have it in a formula, then this should be a bit cleaner than the above:
amt = km * r1 +
( km > 100 ?
km > 250 ?
150 * r2 + (km - 250) * r3 - (km - 100) * r1 :
(km - 100) * (r2 - r1) :
0 ); /* readblity */
Although I don't understand why if statements are bad. It's more readable and has the same performance.