Question

我真的很好奇，因为如何限制像计算器这样的程序中的字符输入，任何人都可以教我如何做，我对此真的很陌生。如果有人回答你，请解释你答案中的每一行代码。提前致谢。：）

#include <iostream>
#include <iomanip>
using namespace std;

int main()
{
    int choice;
    double add, sub, mul, div, rem, square, power, v1, v2;
    long double sine, cosine, tangent;  
    do{
        cout << "Choose an operation." << endl << "\n";
        cout << "[1] Addition." << endl;
        cout << "[2] Subtraction." << endl;
        cout << "[3] Multiplication." << endl;
        cout << "[4] Division." << endl;
        cout << "[5] Exit." << endl;
        cin >> choice;
    while (choice < 1 || choice > 5){
        cout << "Please Choose from 1 to 5" << endl;
        cin >> choice;
    }
if (choice == 1){
    cout << "Please Enter 1st value: ";
    cin >> v1;

    cout << "Please Enter 2nd value: ";
    cin >> v2;

    add = v1 + v2;
    cout << "The answer is: " << fixed << setprecision(2) << add << endl << endl;   
}
else if (choice == 2){
    cout << "Please Enter 1st value: ";
    cin >> v1;

    cout << "Please Enter 2nd value: ";
    cin >> v2;

    sub = v1 - v2;
    cout << "The answer is: " << fixed << setprecision(2) << sub << endl << endl;
}
if (choice == 3){
    cout << "Please Enter 1st value: ";
    cin >> v1;

    cout << "Please Enter 2nd value: ";
    cin >> v2;

    mul = v1 * v2;

    cout << "The answer is: " << fixed << setprecision(2) <<  mul << endl << endl;
}
if (choice == 4){
    cout << "Please Enter 1st value: ";
    cin >> v1;

    cout << "Please Enter 2nd value: ";
    cin >> v2;

    div = v1 / v2;
    rem = fmod (v1,v2);

    cout << "The answer is: " << fixed << setprecision(2) << div << " remainder " << rem << endl << endl;
}
if (choice == 5)
    break;  
}
while (choice != 5);
{
    cout << endl << "Goodbye.";
}
return 0;

}

Answer 1

检查您正在使用的功能the documentation。

简化代码：

double v1;
std::cin >> v1;

这是试图从double中提取std::cin，跳过前导空格。

如果提取失败 - 例如因为某人输入了不代表double值的东西 - 写了零（因为C ++ 11，之前的值保持不变），和failbit在流上设置。

可以检查并清除：

if ( std::cin.fail() )
{
    // handle error
    std::cin.clear();
}

实际上clear()上的页面有一个功能齐全的例子，可以读取数字，检查失败并重复输入。

话虽如此，我还是第二次@ Maikel的评论。如果你想超越实验阶段，你需要编写一个真正的语法分析器，Boost.Spirit是一个很好的选择。

限制C ++中的字符输入

1 个答案: