我的任务是创建一个基于菜单的程序，以使用用户定义的函数计算多个形状的面积。当用户输入字符而不是数字时，我的代码会创建无限循环。我应该怎么办？另外，我想如果有人可以评估我的代码，我应该更改或修改什么吗？我还是 C++ 新手。
输入: 1. 一个 2.j
#include <iostream>
#include <cmath>
using namespace std;
float Circle(double r1);
float Rectangle(double length, double width);
float Triangle(float s1, float s2, float s3);
float Cylinder(double height, double r2);
float Square(double l1, double l2);
int main()
{
char o, d;
do
{//List of what shapes the program can calculate
cout << " Calculator for area of shapes " << endl;
cout << endl;
cout << " List of Area: " << endl;
cout << " A. Circle " << endl;
cout << " B. Rectangle " << endl;
cout << " C. Triangle " << endl;
cout << " D. Cylinder " << endl;
cout << " E. Square " << endl;
cout << " X. Exit " << endl;
cout << endl;
//Choose what shape to calculate
cout << " Please enter the area you wish to calculate: ";
cin >> o;
cout << endl;
//Program determine what calculation to use
switch (o)
{
case 'a'://For Circle
case 'A':
double r1;
while (true)
{
cout << " Radius of Circle: ";
cin >> r1;
if (r1 > 0)
{
Circle(r1);
cout << endl;
break;
}
else
{// If the input is less than 0 an error message will occur and user need to reinput the data
cout << " ERROR! NOT A CIRCLE. Please input value more than 0." << endl;
}
}
break;
case 'b'://For Rectangle
case 'B':
double length, width;
while (true)
{
cout << " Length of Rectangle: ";
cin >> length;
cout << " Width of Rectangle: ";
cin >> width;
if (length > 0 && width > 0)
{
Rectangle(length, width);
cout << endl;
break;
}
else
{
cout << " ERROR! Not A Rectangle. Please input value more than 0 " << endl;
}
}
case 'c'://For Triangle
case 'C':
float s1, s2, s3;
while (true)
{
cout << " Length of side A: ";
cin >> s1;
cout << " Length of side B: ";
cin >> s2;
cout << " Length of side C: ";
cin >> s3;
if ((s1 + s2) > s3 && (s2 + s3) > s1 && (s3 + s1) > s2)
{
Triangle(s1, s2, s3);
cout << endl;
break;
}
else
{
cout << " ERROR!!! NOT A TRIANGLE. Please input value more than 0 " << endl;
}
}
case 'd'://For Cylinder
case 'D':
double height, r2;
cout << " Radius of Cylinder: ";
cin >> r2;
cout << "Height of Cylinder: ";
cin >> height;
while (true)
{
if (r2 > 0 && height > 0)
{
Cylinder(height, r2);
break;
}
else
{
cout << " ERROR!!! NOT A CYLINDER. Please input value more than 0 " << endl;
}
}
case 'e'://For Square
case 'E':
double l1, l2;
while (true)
{
cout << " Length of side 1: ";
cin >> l1;
cout << " Length of side 2: ";
cin >> l2;
if (l1 > 0 && l2 > 0)
{
Square(l1, l2);
break;
}
else
{
cout << " ERROR!!! NOT A SQUARE. " << endl;
}
}
case 'x':
case 'X'://Program end
cout << " ---- PROGRAM END ---- ";
exit(0);
default: // Error message occur if user don't
cout << " ERROR!! PLEASE INPUT RIGHT LETTER ";
cout << endl;
}
// user can choose to use program again or not
cout << " Do you wish to continue using the calculator?(Y/N): ";
cin >> d;
cout << endl;
} while (d == 'y' || d == 'Y');
if (d == 'n' || d == 'N')
{
cout << " ---- PROGRAM END ---- ";
}
return 0;
}
float Circle(double r1)//Calculation for Circle
{
double area;
const double pi = 3.14;
area = pi * (r1 * r1); //Formula for area of Circle
cout << " Area of Circle: " << area;
cout << endl;
return 0;
}
float Rectangle(double length, double width)//Calculation for Rectangle
{
double area;
area = length * width;//Formula for area of Rectangle
cout << " Area of Rectangle: " << area;
cout << endl;
return 0;
}
float Triangle(float s1, float s2, float s3)//Calculation for Triangle
{
float area, s;
s = (s1 + s2 + s3) / 2;
area = sqrt(s * (s - s1) * (s - s2) * (s - s3));//Formula for area of Triangle
cout << " Area of triangle: " << area << endl;
cout << endl;
return 0;
}
float Cylinder(double height, double r2)//Calculation for Cylinder
{
double area;
const double pi = 3.14;
area = 2 * pi * r2 * (r2 + height);//Formula for area of Cylinder
cout << endl;
return 0;
}
float Square(double l1, double l2)//Calculation for Square
{
double area;
area = l1 * l2;//Formula for area of Square
cout << " Area of Square: " << area << endl;
cout << endl;
return 0;
}
最佳答案
与 float r1; cin >> r1; 和非数字输入，输入不会消耗任何内容。重复 cin >> r1 会导致无限循环。
要做什么？
- 检查
cin >> r1是否成功:if (cin >> r1) {/* process r1 */} - 如果不成功，请执行某些操作来处理错误的输入:
else { cin.clear(); cin.ignore(); }
Sets the stream error state flags by assigning them the value of state. By default, assigns std::ios_base::goodbit which has the effect of clearing all error state flags.
Extracts and discards characters from the input stream until and including delim.
示例:
#include <iostream>
#include <limits>
int main()
{
double value = 0.0;
for (;;) {
std::cout << "Value: ";
if (std::cin >> value) {
break; // success -> bail out of loop
} else {
std::cerr << "Wrong input!\n";
std::cin.clear(); // reset state
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // consume wrong input
}
}
std::cout << "Value: " << value << '\n';
return 0;
}
输出:
Value: <b>Hello</b><kbd>↵</kbd>
Wrong input!
Value: <b>1.23</b><kbd>↵</kbd>
Value: 1.23
关于C++ 初学者输入错误数据类型时的无限循环并帮助评估我的代码，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/52905901/