Unexpected output using if-else control structure - c++

Question

When providing the program shown below the input -1.3 and -1.1 for the low and high values, respectively, it prints the error message "Error: high gallon value must be larger than or equal to the low gallon value.". However, the test for this error is if(lowGallon > highGallon), which in this given case it clearly is not. What is the explanation for this output error?
The specific section where this input validation is located is under the section with the comment //checking for numerical input errors.
#include <iostream>
#include <iomanip>
using namespace std;
int main() {
double lowGallon,
highGallon,
literConvert;
const int INCREMENTER = 1;
char charVal;
bool quitting = false,
lowIsNeg = false,
highIsNeg = false,
highIsLessThanLow = false;
cout << "This program creates a gallons to liters conversion table." << endl << endl;
do {
cout << "Enter the lowest gallon value to display (q to quit): ";
cin >> lowGallon;
cout << endl;
do {
//checking for data type input errors
if (cin.fail()) {
cin.clear();
cin >> charVal;
if (charVal == 'q') {
quitting = true;
cout << endl << "Aborting; no conversion performed." << endl;
} else {
cout << "You entered an illegal character: (" << charVal << ")" << endl << endl;
cout << "Enter the lowest gallon value to display (q to quit): ";
cin >> lowGallon;
cout << endl;
}
}
} while (cin.fail() && quitting == false);
if (quitting == false) {
lowGallon = static_cast<int>(lowGallon);
cout << "Enter the highest gallon value to display (q to quit): ";
cin >> highGallon;
cout << endl;
do {
//checking for data type input errors
if (cin.fail()) {
cin.clear();
cin >> charVal;
if (charVal == 'q') {
quitting = true;
cout << endl << "Aborting; no conversion performed." << endl;
} else {
cout << "You entered an illegal character: (" << charVal << ")" << endl << endl;
cout << "Enter the highest gallon value to display (q to quit): ";
cin >> highGallon;
cout << endl;
}
}
} while (cin.fail() && quitting == false);
//checking for numerical input errors
if (quitting == false) {
cout << endl;
if(lowGallon < 0) {
cout << "Error: low gallon value must not be negative." << endl;
lowIsNeg = true;
} else {
lowIsNeg = false;
}
if(highGallon < 0) {
cout << "Error: high gallon value must not be negative." << endl;
highIsNeg = true;
} else {
highIsNeg = false;
}
if(lowGallon > highGallon) {
cout << "Error: high gallon value must be larger than or equal to the low gallon value." << endl;
highIsLessThanLow = true;
} else {
highIsLessThanLow = false;
}
}
if (quitting == false && lowIsNeg == false && highIsNeg == false && highIsLessThanLow == false) {
if (highGallon - static_cast<int>(highGallon) > 0) {
highGallon = static_cast<int>(highGallon) + 1;
}
cout << fixed << setprecision(1) << "The conversion table will be created for the gallon range" << endl;
cout << "of " << lowGallon << " to " << highGallon << " in increments of " << static_cast<double>(INCREMENTER) << endl << endl;
cout << " GALLONS TO LITERS" << endl;
cout << " CONVERSION TABLE" << endl;
cout << " Gallons " << "Liters" << endl;
cout << " ======= " << "=======" << endl;
for(int counter = lowGallon; counter <= highGallon; counter += INCREMENTER) {
cout << setw(9) << setprecision(1) << static_cast<double>(counter);
literConvert = counter * 3.785;
cout << setw(11) << setprecision(3) << literConvert << endl;
}
} else if (quitting == false) {
cout << "Please re-enter low and high gallon values correctly." << endl << endl << endl;
}
}
} while(quitting == false && (lowIsNeg == true || highIsNeg == true || highIsLessThanLow == true));
return 0;
}

Answer 1

In your code you do
lowGallon = static_cast<int>(lowGallon);
which truncates the lowGallon value from -1.3 to -1.0. But you never truncate highGallon value.
The rest follows. -1.0 is indeed greater than -1.1, hence the error message.
Why are you doing this? What's the point of that intermediate conversion to int?