C++程序将'*'读作'a'

Question

我正在研究一个简短的小计算器程序,它接受命令行参数并执行相关操作.这一切都很好,除了乘法.

当我在命令行中键入"./calc 3*3"时,程序会发出错误,当我"cout"它存储为运算符的char时,它会显示"a".所有其他运营商都运作良好.

你们能弄明白为什么它不接受"*"作为一个字母吗？

这是代码和一些示例输出:

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

const int MINIMUM_ARGUMENTS = 4; //must have at least 4 arguments: execution command, a first number, the operator, and a second number;

double Add(double x, double y);
double Subtract(double x, double y);
double Multiply(double x, double y);
double Divide(double x, double y);

int main(int argc, char* argv[])
{
    if (argc < MINIMUM_ARGUMENTS) //"less than" because counting execution command as first argument
    {
        cout << "\nMust have at least " << MINIMUM_ARGUMENTS << " arguments (including execution command)." << endl;
    }
    else
    {
        double num1 = atof(argv[1]); //stores first argument as double
        char operation = *argv[2]; //stores second argument (operator) as char
        double num2 = atof(argv[3]); //stores third argument - second number
        double result = 0; //will store result of arithmetic    

        cout << '\n';

        switch (operation) //determines which function to call based on the char (operator) argument
        {
        case '+':
            result = Add(num1, num2);
            cout << result << endl;
            break;
        case '-':
            result = Subtract(num1, num2);
            cout << result << endl;
            break;
        case '*':
            result = Multiply(num1, num2);
            cout << result << endl;
            break;
        case '/':
            result = Divide(num1, num2);
            cout << result << endl;
            break;
        default:
            cout << "Error." << endl;           
        }   
    }

    cin.clear();
    cout << "\nPress enter to quit." << endl;
    cin.ignore();

    return 0;
}

double Add(double x, double y)
{
    return x + y;
}

double Subtract(double x, double y)
{
    return x - y;
}

double Multiply(double x, double y)
{
    return x * y;
}

double Divide(double x, double y)
{
    return x / y;
}

样本输出:

-bash-4.1$ ./calc 10 - 5

5

Press enter to quit.

-bash-4.1$ ./calc 4 + 9

13

Press enter to quit.

-bash-4.1$ ./calc 10 / 2

5

Press enter to quit.

-bash-4.1$ ./calc 5 * 5

Error.

Press enter to quit.

Answer 1

操作系统(bash here)使用*符号从当前目录中选择所有文件.所以改变你的标志.

我建议'x'

Answer 2

发送时*使用单引号'*'或使用它来转义它\*.

只需*将无法工作,因为在命令行中*的意思是"在当前目录中的一切."