c++ - IF 或 WHILE 用于数字输入检查器

Question

我一直在开发一个程序来计算用户输入的平均值。我还不知道输入检查器要用什么。我还不能使用数组或字符串。如何检查两个输入是否都是数值？如果他们不是；如何再次询问正确的输入？

#include <iostream>
using namespace std;
int main()
{
    // Get number from user
    int input = 0;
    double accumulator = 0;
    double mean;
    cout << "How many numbers would you like me to average together?\n";
    cin >> input;
    if (input >= 0){ //to check if input is a numerical value

        // Compute and print the mean of the user input

        int number = 1;
        double x;
        while (number <= input) //while corrected
        {
            cout << "Please type a numerical value now: \n";
            cin >> x;
            if (x < 0  || x > 0){ //to check if x is a numerical value
                accumulator = accumulator + x;
            }
            else {
                cout << "Input incorrect"<< endl;
            }
            number = number + 1;
        }
        mean = accumulator / input; // formula corrected
        cout << "The mean of all the input values is: " << mean << endl;
        cout << "The amount of numbers for the average calculation is: " << input << endl;
        }
    else {
        cout << "Input incorrect"<< endl;
    }
    return 0;
}

Answer 1

您可以使用 cin.fail检查错误。请注意，如果用户输入数字后跟字母，可以说 123abc , 然后 x将存储为 123但是abc保留在输入缓冲区中。您可能希望立即清除它 abc不会出现在下一个循环中。

while (number <= input) //while corrected
{
    cout << "Please type a numerical value now: \n";
    cin >> x;

    bool error = cin.fail();
    cin.clear();
    cin.ignore(0xFFFF, '\n');

    if (error) 
    { 
        cout << "Input incorrect" << endl;
        continue;
    }

    accumulator = accumulator + x;
    number = number + 1;
}

或者你可以初始化x .例如

double x = numeric_limits<double>::min();
cin >> x;
cin.clear();
cin.ignore(0xFFFF, '\n');

if (x == numeric_limits<double>::min())
{ 
    cout << "Input incorrect" << endl;
    continue;
}

如果发生错误则x保持不变并且您知道出现错误，因为用户输入的数字不太可能与 numeric_limits<double>::min() 匹配

与此问题无关，但您还应该考虑被零除的错误。

if (input == 0)
    mean = 0;//avoid divide by zero, print special error message
else
    mean = accumulator / input;