c# - 在“if”语句之外访问变量

Question

我怎样才能insuranceCost在if声明之外提供？

if (this.comboBox5.Text == "Third Party Fire and Theft")
{
    double insuranceCost = 1;
}

Answer 1

在 if 语句之外定义它。

double insuranceCost;
if (this.comboBox5.Text == "Third Party Fire and Theft")
        {
          insuranceCost = 1;
        }

如果您从方法中返回它，那么您可以为其分配默认值或 0，否则您可能会收到错误“使用未分配的变量”；

double insuranceCost = 0;

或者

double insuranceCost = default(double); // which is 0.0

Answer 2

除了其他答案之外，您可以if在这种情况下内联（仅为清楚起见添加括号）：

double insuranceCost = (this.comboBox5.Text == "Third Party Fire and Theft") ? 1 : 0; 

如果条件不匹配，则替换0为您要初始化的任何值。insuranceCost

Answer 3

    double insuranceCost = 0; 
    if (this.comboBox5.Text == "Third Party Fire and Theft") 
    { 
        insuranceCost = 1; 

    } 

在 if 语句之前声明它，并给出一个默认值。在 if 中设置值。如果你不给双精度值一个默认值，你会在编译时得到一个错误。例如

double GetInsuranceCost()
{
        double insuranceCost = 0; 
        if (this.comboBox5.Text == "Third Party Fire and Theft") 
        { 
            insuranceCost = 1; 

        } 
        // Without the initialization before the IF this code will not compile
        return insuranceCost;
}