If-Else nest redundant? - c++

Question

Currently, I am taking a C++ course at my local college, and was given a debugging assignment. In the instructions for this assignment, I was told that the only thing really wrong with this code, is that the conditions for the nested if-else-if statements on lines 82-89 are redundant, however, I cannot see another way to get the same results without having those conditions stay the same...any tips or such would be greatly appreciated!
#include <iostream>
#include <conio.h>
#include <iomanip>
using namespace std;
const int BASE_COST = 10;
const int LOW_LIMIT = 20;
const int MID_LIMIT = 40;
const int HIGH_LIMIT = 60;
const double LOW_CHECKS = .10;
const double MIDLOW_CHECKS = .08;
const double MIDHIGH_CHECKS = .06;
const double HIGH_CHECKS = .04;
int main()
{
int numOfChecks;
double multiplierValue;
double totalFee;
cout << fixed << showpoint;
cout << setprecision(2);
cout << "Please enter the number of checks you used this month: ";
cin >> numOfChecks;
if(numOfChecks < 0)
{
cout << "Number of checks can't be negative. Program ends.\n";
exit(1); //terminate the program with error code 1
}
//the following line runs only if the program did not terminate, so start over if-else
if(numOfChecks < LOW_LIMIT)
multiplierValue = LOW_CHECKS;
else if(numOfChecks < MID_LIMIT)
multiplierValue = MIDLOW_CHECKS;
else if(numOfChecks >= MID_LIMIT && numOfChecks < HIGH_LIMIT)
multiplierValue = MIDHIGH_CHECKS;
else if (numOfChecks >= HIGH_LIMIT)
multiplierValue = HIGH_CHECKS;
totalFee = BASE_COST + numOfChecks * multiplierValue;
cout << "Your total for this month is $" << totalFee;
_getch();
return 0;
}

Answer 1

This part else if(numOfChecks >= MID_LIMIT && numOfChecks < HIGH_LIMIT) looks redundant. Provided you keep the order of the range checks, it can be simplified to just else if (numOfChecks < HIGH_LIMIT), same as the one following it (which is just not needed) so that the whole piece looks like:
//the following line runs only if the program did not terminate, so start over if-else
if (numOfChecks < LOW_LIMIT)
multiplierValue = LOW_CHECKS;
else if (numOfChecks < MID_LIMIT)
multiplierValue = MIDLOW_CHECKS;
else if (numOfChecks < HIGH_LIMIT)
multiplierValue = MIDHIGH_CHECKS;
else
multiplierValue = HIGH_CHECKS;

Answer 2

Indeed, all the conditions are redundant: use an algorithm :)
Live On Coliru
#include <iomanip>
#include <map>
#include <iostream>
namespace {
using Threshold = unsigned;
using Rate = double;
static Rate constexpr BASE_COST = 10.0;
std::map<Threshold, Rate, std::greater<> > const tariffs {
{ 0, .10},
{20, .08},
{40, .06},
{60, .04},
};
double fee(unsigned numOfChecks) {
auto rate = tariffs.lower_bound(numOfChecks);
return BASE_COST + rate->second * numOfChecks;
}
}
int main() {
unsigned numOfChecks;
std::cout << "Please enter the number of checks you used this month: ";
if (std::cin >> numOfChecks) {
std::cout
<< "\nYour total for this month is $"
<< std::fixed << std::showpoint << std::setprecision(2) << fee(numOfChecks)
<< std::endl;
} else {
std::cout << "Invalid input\n";
return 1;
}
}
Prints e.g.
Please enter the number of checks you used this month: 10
Your total for this month is $11.00
Please enter the number of checks you used this month: 20
Your total for this month is $11.60
Please enter the number of checks you used this month: 30
Your total for this month is $12.40
Please enter the number of checks you used this month: 40
Your total for this month is $12.40
Please enter the number of checks you used this month: 50
Your total for this month is $13.00
Please enter the number of checks you used this month: 60
Your total for this month is $12.40
Please enter the number of checks you used this month: 70
Your total for this month is $12.80
Please enter the number of checks you used this month: 80
Your total for this month is $13.20
Please enter the number of checks you used this month: 90
Your total for this month is $13.60
Please enter the number of checks you used this month: 100
Your total for this month is $14.00