C++ if 语句问题 - 显示错误信息

Question

我的程序在显示不应该显示的不同 if 语句中的信息时遇到问题。 http://i53.tinypic.com/1zyx68.png

#include <iostream>
#include <string>
using namespace std;
int main( )
{
    string smreturn = "";
    string jointsingle = "";
    double income = 0.00;
double taxedincome = 0.00;
{
cout << "\nPlease enter your taxable income: ";
cin >> income;
while (income <= 0)
{
    cout << "\n Please enter a valid positive taxable income: ";
    cin >> income;
}
cout << "\n";
cout << "\nPlease press m if married and filing for a joint return, or s if filing for a single return: ";
cin >> smreturn;
            while (!(smreturn =="m") && !(smreturn =="M") && !(smreturn =="s") && !(smreturn =="S"))
{
    cout << "\nPlease press m if married and filing for a joint return,\n or s if filing for a single return: ";
    cin >> smreturn;
}

if (smreturn == "m" || "M")
{
    if (income >= 0 && income <= 1726)
    {
        taxedincome = income * .023;
    }
    if (income >= 1727 && income <= 3450)
    {
        taxedincome = (income - 1727) * .033 + 40;
    }
    if (income >= 3451 && income <= 5176)
    {
        taxedincome = (income - 3450) * .042 + 97;
    }
    if (income >= 5177 && income <= 6900)
    {
        taxedincome = (income - 5176) * .052 + 169;
    }
    if (income > 8626)
    {
        taxedincome = (income - 8626) * .07 + 362;
    }
        cout << "\nYour taxable income is:$" << (income);
cout << "\nAnd you are filing a joint return";
cout << "\nYour income tax will be:$" << (taxedincome);
cout << "\n";

}
if (smreturn == "s"||"S")
{
    if (income >= 0 && income <= 863)
    {
        taxedincome = (income * .023);
    }
    if (income >= 864 && income <= 1726)
    {
        taxedincome = (income - 863) * .033 + 20;
    }
    if (income >= 1727 && income <= 2588)
    {
        taxedincome = (income - 1726) * .042 + 48;
    }
    if (income >= 2589 && income <= 3450)
    {
        taxedincome - (income - 2588) * 0.052 + 85;
    }
    if (income >= 3451 && income <= 4313)
    {
        taxedincome - (income - 3450) * 0.06 + 129;
    }
    if (income > 4313)
        {
            taxedincome - (income - 4313) * 0.07 + 181;
}
        cout << "\nYour taxable income is:$" << (income);
cout << "\nAnd you are filing a single return";
cout << "\nYour income tax will be:$" << (taxedincome);
cout << "\n";
}
}           cout << "\n";
string returninfo;
if (smreturn == "s" || "S")
{
    returninfo == "single return";
}
else
{
    returninfo == "joint return";
}

system("PAUSE");
return 0;
}

它显示来自两个 If 的信息报表，将纳税收入作为单一申报表保存为联合申报表。

Answer 1

if (smreturn == "m" || "M")

应该是

if ( (smreturn == "m") || (smreturn == "M") )

在其他情况下很少会出现类似的错误。如果需要比较，则需要对 if 条件中的每个标识符重复进行比较。

Answer 2

你的 if 语句是错误的：

if (smreturn == "m" || "M")

试试这个：

if ((smreturn == "m") || (smreturn == "M"))

这个语句有同样的问题：

if (smreturn == "s"||"S")

以同样的方式修复它。

Answer 3

您的错误在于：

if (smreturn == "m" || "M")

使用 || 时需要创建两个条件（或者）。示例：

if (age == 15 || yearOfBirth == 1996) {
    std::cout << "Happy!" << std::endl;
} else {
    std::cout << "Sad!" << std::endl;
}

您可以使用 && (AND) 在相同模式下。

建议：

不要使用

using namespace std;

这不是一个好的做法。您将使用的 STD 的每个函数

std::function

示例：

std::cout << "Hello World" << std::endl;

“endl”是清除缓冲区并添加“\n”。

Answer 4

smreturn == "m" || “M” 始终为 true，因为 “M” 将隐式转换为 true。

您可能想要 smreturn == "m" || smreturn == "M" 。

Answer 5

您可能的意思是：

if ((smreturn == "m") || (smreturn == "M"))

相等运算符测试相等性。您将其用作一种集合成员资格测试。如果能够编写就太好了

if (smreturn in ["m","M"])

，但那是高级语言的保留。