C#用Math.Round和double.TryParse方法实现四舍五入

目录

一、涉及到的知识点

1.double.TryParse（）方法

2.Math.Round(Decimal, Int32)?? 方法

3.comboBox1没有选项

二、示例

1.源码

2.生成

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一、涉及到的知识点

1.double.TryParse（）方法

? ? ? ? ?详见本文作者写的其他文章，

????????C#用double.TryParse(String, Double)方法将字符串类型数字转换为数值类型-CSDN博客 ?https://wenchm.blog.csdn.net/article/details/135593983

2.Math.Round(Decimal, Int32)?? 方法

????????将小数值舍入到指定数量的小数位，并将中点值舍入到最接近的偶数。

public static decimal Round (decimal d, int decimals);

参数
d
Decimal
要舍入的小数。

decimals
Int32
返回值中的小数位数。

返回
Decimal
最接近 d 的 decimals 位小数的数字。

例外
ArgumentOutOfRangeException
decimals 小于 0 或大于 28。

OverflowException
结果超出了 Decimal 的范围。

注解
参数的值 decimals 范围为 0 到 28。此方法使用 的默认舍入约定 MidpointRounding.ToEven。在舍入中点值时，舍入算法执行相等测试。

//示例
Console.WriteLine(Math.Round(3.44m, 1));
Console.WriteLine(Math.Round(3.45m, 1));
Console.WriteLine(Math.Round(3.46m, 1));
Console.WriteLine();

Console.WriteLine(Math.Round(4.34m, 1));
Console.WriteLine(Math.Round(4.35m, 1));
Console.WriteLine(Math.Round(4.36m, 1));

// The example displays the following output:
//       3.4
//       3.4
//       3.5
//
//       4.3
//       4.4
//       4.4

3.comboBox1没有选项

?????????当没有选项时，comboBox1!.SelectedIndex == -1；

二、示例

1.源码

//用Math.Round和double.TryParse方法实现四舍五入
namespace _048
{
    public partial class Form1 : Form
    {
        private TextBox?textBox1;
        private TextBox? textBox2;
        private Label?label1;
        private Label? label2;
        private TextBox? textBox3;
        private ComboBox? comboBox1;
        private Button? button1;

        public Form1()
        {
            InitializeComponent();
            Load += Form1_Load;
        }
        private void Form1_Load(object?sender, EventArgs e)
        {
            // 
            // textBox1
            // 
            textBox1 = new TextBox
            {
                Location = new Point(12, 12),
                Name = "textBox1",
                Size = new Size(100, 23),
                TabIndex = 0
            };
            // 
            // textBox2
            //           
            textBox2 = new TextBox
            {
                Location = new Point(137, 12),
                Name = "textBox2",
                Size = new Size(100, 23),
                TabIndex = 1
            };
            // 
            // label1
            //          
            label1 = new Label
            {
                AutoSize = true,
                Location = new Point(116, 18),
                Name = "label1",
                Size = new Size(17, 17),
                TabIndex = 2,
                Text = "+"
            };
            // 
            // label2
            //          
            label2 = new Label
            {
                AutoSize = true,
                Location = new Point(12, 82),
                Name = "label2",
                Size = new Size(68, 17),
                TabIndex = 3,
                Text = "计算结果："
            };
            // 
            // textBox3
            //          
            textBox3 = new TextBox
            {
                Location = new Point(137, 76),
                Name = "textBox3",
                Size = new Size(100, 23),
                TabIndex = 4
            };
            // 
            // comboBox1
            //           
            comboBox1 = new ComboBox
            {
                FormattingEnabled = true,
                Location = new Point(12, 47),
                Name = "comboBox1",
                Size = new Size(100, 25),
                TabIndex = 5,
                
        };
            comboBox1.Items.AddRange([
            "保留1位小数",
            "保留2位小数",
            "保留3位小数",
            "保留4位小数"]);
            // 
            // button1
            // 

            button1 = new Button
            {
                Location = new Point(162, 44),
                Name = "button1",
                Size = new Size(75, 23),
                TabIndex = 6,
                Text = "计算",
                UseVisualStyleBackColor = true
            };
            button1.Click += Button1_Click;
            // 
            // Form1
            // 
            AutoScaleDimensions = new SizeF(7F, 17F);
            AutoScaleMode = AutoScaleMode.Font;
            ClientSize = new Size(250, 107);
            Controls.Add(button1);
            Controls.Add(comboBox1);
            Controls.Add(textBox3);
            Controls.Add(label2);
            Controls.Add(label1);
            Controls.Add(textBox2);
            Controls.Add(textBox1);
            Name = "Form1";
            Text = "四舍五入";   
        }

        private void Button1_Click(object? sender, EventArgs e)
        {
            if(textBox1!.Text !=""&& textBox1!.Text != "")
            {
                if(comboBox1!.SelectedIndex != -1)
                {
                    if (double.TryParse(textBox1!.Text, out double temp1) &&
                            double.TryParse(textBox2!.Text, out double temp2))
                    {
                        textBox3!.Text = //得到四舍五入后的值
                            Math.Round(temp1 + temp2, comboBox1!.SelectedIndex + 1).ToString();
                    }
                    else
                    {
                        MessageBox.Show("输入数值不正确！", "提示！");
                    }
                }
                else
                    MessageBox.Show("请选择正确的小数点后位数", "提示！");
            }
            else
                MessageBox.Show("重新输入正确的数字！", "提示！");
        }
    }
}

2.生成

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