1.VS2019创建C#主程序

2.编译主程序

debug目录下生成exe：

3.添加类库工程，并添加计算逻辑

添加计算逻辑：

namespace Calculate
{public class CalculateAssistant{// +public double Sum(double a, double b){return a + b;}public Int64 Sum(Int64 a, Int64 b){return a + b;}// -public double Sub(double a, double b){return a - b;}public Int64 Sub(Int64 a, Int64 b){return a - b;}// *public double Multiple(double a, double b){return a * b;}public Int64 Multiple(Int64 a, Int64 b){return a * b;}// /public double Divide(double a, double b){return a / b;}public Int64 Divide(Int64 a, Int64 b){return a / b;}}
}

4.给主程序添加引用项

5.重新编译主程序

先生成依赖项目，再生成主程序：

debug目录增加了dll文件：

6.主程序添加测试逻辑

using Calculate;

namespace Main
{public partial class Form1 : Form{public Form1(){InitializeComponent();}private void Add_Click(object sender, EventArgs e){Calculate.CalculateAssistant calc = new CalculateAssistant();double result = calc.Sum(double.Parse(textBox1.Text),double.Parse(textBox2.Text));textBox3.Text = result.ToString();            }private void Sub_Click(object sender, EventArgs e){Calculate.CalculateAssistant calc = new CalculateAssistant();double result = calc.Sub(double.Parse(textBox1.Text), double.Parse(textBox2.Text));textBox3.Text = result.ToString();}private void Multi_Click(object sender, EventArgs e){Calculate.CalculateAssistant calc = new CalculateAssistant();double result = calc.Multiple(double.Parse(textBox1.Text), double.Parse(textBox2.Text));textBox3.Text = result.ToString();}private void Divide_Click(object sender, EventArgs e){Calculate.CalculateAssistant calc = new CalculateAssistant();double result = calc.Divide(double.Parse(textBox1.Text), double.Parse(textBox2.Text));textBox3.Text = result.ToString();}}
}