C#中解析转换字符串后仍无法使用乘法运算符的问题

错误原因 #

你调用int.Parse()或Convert.ToInt32()时，只是执行了转换操作，但没有将转换后的整数结果赋值给新变量。原变量User_Length和User_Width始终是string类型，而C#不允许对字符串直接使用乘法运算符，因此触发Operator '*' cannot be applied to operands of type 'string' and 'string'错误。

修正后的代码 #

using System;
                    
public class Program
{
    public static void Main()
    {
        Console.WriteLine("Hello, would you like me to calculate the area of your rectangle? input anything to continue.");
        Console.ReadLine();
        
        Console.WriteLine("Please give me the Length of the rectangle:");
        // 将输入转换为整数并保存到int类型变量
        int length = int.Parse(Console.ReadLine());
        
        Console.WriteLine("Please give me the Width of your rectangle");
        int width = Convert.ToInt32(Console.ReadLine());
        
        // 使用整数变量计算面积
        Console.WriteLine("Here is the Area of your rectangle: " + (length * width));
    }
}

关键修改点 #

• 将用户输入的字符串直接转换为整数并赋值给int类型变量（length和width），不再保留多余的字符串变量
• 计算面积时使用整数变量进行乘法运算，避免字符串类型的错误

额外建议：添加输入验证 #

如果用户输入非数字内容，int.Parse()会抛出异常，建议使用int.TryParse()做输入验证，提升程序稳定性：

using System;
                    
public class Program
{
    public static void Main()
    {
        Console.WriteLine("Hello, would you like me to calculate the area of your rectangle? input anything to continue.");
        Console.ReadLine();
        
        int length;
        while (true)
        {
            Console.WriteLine("Please give me the Length of the rectangle:");
            if (int.TryParse(Console.ReadLine(), out length))
            {
                break;
            }
            Console.WriteLine("Invalid input, please enter a number.");
        }
        
        int width;
        while (true)
        {
            Console.WriteLine("Please give me the Width of your rectangle");
            if (int.TryParse(Console.ReadLine(), out width))
            {
                break;
            }
            Console.WriteLine("Invalid input, please enter a number.");
        }
        
        Console.WriteLine("Here is the Area of your rectangle: " + (length * width));
    }
}

内容的提问来源于stack exchange，提问作者Dima