当分别为低值和高值提供输入-1.3和-1.1的程序时，它会输出错误消息“错误：高加仑值必须大于或等于低加仑值”。但是，此错误的测试是if(lowGallon > highGallon)，在这种情况下，它显然不是。//checking for numerical input errors。这个输出错误的解释是什么？
此输入验证所在的特定部分位于注释#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;
}
。
{{1}}
答案 0 :(得分：1)
在您的代码中
lowGallon = static_cast<int>(lowGallon);
将lowGallon值从-1.3截断为-1.0。但是你永远不会截断highGallon值。
其余的如下。 -1.0确实大于-1.1，因此错误消息。
你为什么要这样做？中间转换为int的重点是什么？