what to use instead of if/else, switch or ternary operators?

Question

just a quick question. I have a school project which I have to solve the problem again as a new separate problem. Provide the tax calculation using only one line of code and without using any if/else or switch statements or using the ternary operator. I may be able to do the calculations i one line of code but I have no idea what to write if I am supposed to get rid of the conditional statements. Below is my code that I am supposed to change. My teacher is kind of picky about what we can use and what not. Also this project was given to us when we hadn't learned functions in all that. I am looking for an answer that is not too higher level, since I am new to c++. /***************************************************************

Write a program for a state that computes tax according to the rate schedule:• No tax on first $15,000 of income• 5% tax on each dollar from $15,001 to $25,000• 10% tax on each dollar over $25,000 ***************************************************************/

   #include <iostream>
        #include <string>
        #include <sstream>
        #include <iomanip>

        using namespace std;
        int main()
        {
            string income2;
            double income;
            const double FIRSTTAX = 500;
            double secondDifference;
            const double FTAX = 0.05;
            const double TTAX = 0.1;
            cout << "Please enter the annual income: $ ";
            getline (cin, income2);
            stringstream (income2)>> income;


                if (income == 0 || income <= 15000 )
                {
                    cout << "No income on first 15000 " << endl;
                }
            else if (income > 15000 && income <= 25000)
                {
                    income = (income - 15000)* FTAX;
                    cout << " Your net income " << income <<endl;

                }
             else if (income > 25000)
                {
                    secondDifference = (income - 25000) * TTAX +(income - 15000- (income - 25000)) * FTAX;



                    cout << " Your net income " << income <<fixed<<setprecision(2) <<endl;

                    cout << " Your tax " << secondDifference <<fixed<<setprecision(2) << endl;
}




        return 0;
    }

You're probably being asked for an algorithmic solution, rather than a syntactic one. — yaakov, Apr 30 '16 at 22:55
See https://stackoverflow.com/questions/2725044/can-i-assume-booltrue-int1-for-any-c-compiler — 9mjb, Apr 30 '16 at 23:16

shrike · Accepted Answer · 2016-04-30T23:30:21.407

1

In one single line:

tax = max(income-15000,0)*FTAX + max(income-25000,0)*(TTAX-FTAX)

edited Apr 30 '16 at 23:30

answered Apr 30 '16 at 23:09

shrike

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@Thomas: are you sure ? 5%+5%=10%, isn't it ? – shrike Apr 30 '16 at 23:12
right approach, but of course the `max` function must itself use a conditional operator of some sort internally – Alnitak Apr 30 '16 at 23:12
@Alnitak I don't think the OP can be held accountable for what runtime functions do internally. – Carey Gregory Apr 30 '16 at 23:14
@Alnitak: "without using any if/else or switch statements or using the ternary operator" ; comparison operators are allowed, branches are not; max() can be implemented without branch. – shrike Apr 30 '16 at 23:16
I meant 'statement' (or 'operation'), not 'operator' – Alnitak Apr 30 '16 at 23:17
@shrike your calculation is brittle to changes in the tax rate – Alnitak Apr 30 '16 at 23:23
@Alnitak: do you prefer it written this way ? – shrike Apr 30 '16 at 23:31

score 0 · Answer 2 · answered Apr 30 '16 at 23:22

0

To account for the two different tax rates, and to allow either tax rate to vary individually:

double lo_thresh = 15000;
double hi_thresh = 25000;

double lo_rate = 0.05;
double hi_rate = 0.10;

double tax = lo_rate * min(hi_thresh - lo_thresh, max(income - lo_thresh, 0)) +
             hi_rate * max(income - hi_thresh, 0);

The first half looks at income in excess of 15k, but caps the amount above that at which that amount applies to 10k (i.e. the difference between the two thresholds).

The second half calculates the higher tax rate due on income above 25k.

answered Apr 30 '16 at 23:22

Alnitak

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imho, `min()` is useless – shrike Apr 30 '16 at 23:33
@Alnitka; yet, my proposal using 2 max, no min, seams to work... or maybe I missed something in the OP's question... – shrike Apr 30 '16 at 23:41
1

It's not useless, it's just a different formulation. This one (IMHO) more accurately describes the rule, i.e "you pay X% tax between A and B, and Y% tax above B". Yours is equivalent, but semantically is closer to "you pay X% tax on _everything_ above A, and (Y-X)% tax _on top of that_ for everything above B" – Alnitak Apr 30 '16 at 23:46
and FWIW, in the UK where I am the HMRC tax calculations are always shown like this - you see how much tax you're paying in the lower band at that rate, and then a separate line for how much you're paying on income in excess of the upper threshold. They never treat the higher rate as an "difference" on top of the lower rate. – Alnitak Apr 30 '16 at 23:52
not exactly, develop the formula and you get: X% between A and B, and Y% above B ; ie: `(max(income-15000,0)-max(income-25000,0))*FTAX + max(income-25000,0)*TTAX` . Anyway, have a good night, bye. – shrike Apr 30 '16 at 23:58
@shrike that's what I said - "X% on _everything_ above A" (thus X% + Y% - X%, i.e. Y% net on everything above B) – Alnitak May 01 '16 at 08:41

what to use instead of if/else, switch or ternary operators?

2 Answers2